I'd suggest a 'gish', a fighter-mage. On one side of the gestalt take something like Fighter or warblade if you have Tome of battle. On the other I'd take psion. Focus on powers which augment your combat capabilities, and you should be good to go.
Phrenic is one of the better +2 LA templates, and it does make you a psionic creature. Bonuses to all your mental ability scores, some decent psi-like abilities, and pretty good SR.
If you're soloing, you'll need Trapfinding (if you suspect your DM will be throwing traps at you). Artificer (Eberron Campaign Setting), Beguiler (PHB2), and Factotum (Dungeonscape) are probably the best places to get it.
If you want psionics from a class, Telepath and Wilder are the best at dealing with social situations (although Telepath would overlap considerably with Beguiler).
Intelligence synergy, various abilities now via psionics and later via Artificer stuff. Getting to craft items so you have what you need, and having a versatile enough base to deal with a variety of situations. After all about the only thing Artificers aren't stellar at is crowd control as they need a staff to do it effectively for the most part, and staves are late game. Psionics covers that. Between these two you can make a self healing gish that can deal with traps, for example.
From Lords of Madness:
“Shadow” is a template that can be added to any corporeal
aberration, animal, dragon, fey, giant, humanoid, magical beast,
monstrous humanoid, plant, undead, or vermin.
...
Alignment: Usually neutral evil.
...
Level Adjustment: Same as base creature +2.
So, NE is the perfect alignment to start as. It's also rather sinister-looking in the book's pictures. Dark and... um... shadowy >.>
There's always the martial rogue from UA...you don't get sneak attack, but you get fighter bonus feats to replace it (tons of feats and trapfinding too ^^ ). All you'd need from there is whatever combat class you want, or you can do something with healing abilities. Druid wouldn't be a bad choice, especially if you use the Spell Compendium for the Vigor spells. Personally, I've always found the 3.5 psionic classes to be a bit underpowered. Metapsionics is great (and easy to use), but the selection of powers just doesn't lend itself to versatility. If I were to recommend one, though, I'd have to point you to the Soulknife. It never runs out of 'ammo', get's a nasty psychic strike that works wonders when you have high amounts of mobility (and also makes up for not having sneak attack), and there's no weapon to buy
I wouldn't recommend the martial rogue. Feats just aren't that powerful-- that's why so many people think the Fighter is weak.
A Psion can be plenty versatile if you pick your powers well. I'd suggest looking at the Psion Buildguide on the Psionics board. Metapsionics aren't as good as metamagic until later levels, because of the way Psionics works. (Empower pays off around level 10, Maximize around level 15. Quicken is nice, but a lot of buffs have augments to turn them into Swift actions anyway.)
Druid is one of the most powerful classes in the game. Druid//Artificer isn't that great, though, because Wild Shape melds your equipment into your body-- equipment the Artificer needs to function.
I wouldn't reccoment the Soulknife either. Its one class feature is "I have a weapon". Well, so does everyone else. Yes, they have to buy one, but they don't have to spend any money shoring up all the Soulknife's weaknesses. (That doesn't mean you shouldn't play one. I've tried one myself and had fun. But it's not a strong class.)
One disadvantage to the Psion//Artificer is that metamagic feats don't help your powers, and metapsionic feats don't help your infusions, scrolls, wands, or staves. You could try a Psionic Artificer, but it's not written very well. Note that both the Expanded Psionics Handbook and the Magic Item Compendium specify that item creation feats are transparent between magic and psionics; Craft Magic Arms and Armor can be used to creat psionic weapons and armor, while Craft Wondrous Item can be used to create miscellaneous psionic items. That might not work for scrolls/power stones, wands/dorjes, or staves/psicrowns; you'll have to ask the DM.
One nice thing about a Psion//Artificer is, if you learn Astral Construct (either by being a Shaper or through Hidden Talent or Expanded Knowledge), your Infusions work on your Astral Construct.
And if you do decide to put the Artificer on one side, you might want to check out the Artificer's Handbook on the CharOp board. Same goes for the Druid Handbook on the CharOp board if you want a Druid on one side.
There's always the martial rogue from UA...you don't get sneak attack, but you get fighter bonus feats to replace it (tons of feats and trapfinding too ^^ ). All you'd need from there is whatever combat class you want, or you can do something with healing abilities. Druid wouldn't be a bad choice, especially if you use the Spell Compendium for the Vigor spells. Personally, I've always found the 3.5 psionic classes to be a bit underpowered. Metapsionics is great (and easy to use), but the selection of powers just doesn't lend itself to versatility. If I were to recommend one, though, I'd have to point you to the Soulknife. It never runs out of 'ammo', get's a nasty psychic strike that works wonders when you have high amounts of mobility (and also makes up for not having sneak attack), and there's no weapon to buy
...Please tell me this is a joke post.
As for soulknife, in the COB intro stuff there's a soulknife handbook that gives some really good info about how to make a psychic-striking mind-blade thrower. It's just massive hit after massive hit (though I think a warlock outdoes it on that specific aspect with just eldritch blast). I've played melee SKs before as well, and I enjoyed them every time. Sure, they weren't the absolute best, but they were fun. Isn't the point of D&D to have fun?
I'm a fan of the 'nuke now, ask questions later' method when it comes to casters, which probably isn't a good style for a psion.
It it's not the best stlye for any caster, but it's even worse for a Psion. Also, that's probably not necessarily the best test of a character's versatility.
I've played melee SKs before as well, and I enjoyed them every time. Sure, they weren't the absolute best, but they were fun. Isn't the point of D&D to have fun?
Pretty much, yes. But the Soulknife isn't a really powerful class. In this thread, we're discussing a single character who gets two sets of class features to tackle a job that usually takes four guys. Spending half his class features to duplicate a 162,000gp item probably isn't the best plan.
Back to the versatility in casters though, I haven't used any psionic classes with gestalt. I also tend to look at offensive options instead of other options within a class' spell/power selection, mostly because I'm used to having a meat shield and a cleric in the party. For just one gestalt being the entire party, there's probably a lot of options I've never seen. I just thought I'd throw out a couple classes I enjoyed ^^
No, it's not a joke post. I've never gotten as much use out of a psion as I have with a sorcerer. I like the power point system and all, but the powers themselves have never been all that useful to me. I've taken a couple psions to 15ish or so, starting anywhere from 1st to 5th, and it just didn't work for me. I'm a fan of the 'nuke now, ask questions later' method when it comes to casters, which probably isn't a good style for a psion.
As for soulknife, in the COB intro stuff there's a soulknife handbook that gives some really good info about how to make a psychic-striking mind-blade thrower. It's just massive hit after massive hit (though I think a warlock outdoes it on that specific aspect with just eldritch blast). I've played melee SKs before as well, and I enjoyed them every time. Sure, they weren't the absolute best, but they were fun. Isn't the point of D&D to have fun?
First, you stated you've found the psionic classes to be underpowered. Some are, but certainly not all. Second, you called a psion 'not very versatile'. Which may be true compared to a wizard, but... They're still technically casters. Nuff said really. Third, you then suggested the Soulknife as a fix to this. The Soulknife is both the weakest psionic class by far, and far less versatile to the point of being a one trick pony.
And the style of 'nuke first, ask questions later' is subpar (read: utter crap) for all casters. Psions are no exception. Unoptimized Fighter does as much damage as you, but every single round. If they're actually trying to hit hard... well you're useless really.
Case in point: Game I'm in now. Barb/Warblade hits in the 20s and 30s every hit. Won't be as optimal later due to reliance on punishing stance and such. Also rolls low a lot, but that's not a proper gauge of effectiveness. It's just bad luck. Duskblade hits around 20 every hit, (no strikes/stances to boost it) and can go as high as 45 or so if he actually uses his spells via channeling. Then there's a battle sorcerer, who for some reason isn't played as a gish at all. Best trick? Scorching Ray. 4d6 for the loss. If the battle sorcerer instead took gish like spells, she could hit hard too. Alternately, normal sorcerer and any spell except direct damage that functions as an encounter winner.
EDIT: I just stumbled across this. Army of One Challenge
What makes nuking such a bad choice? I had a gestalt wiz/sor build that used Force Missile Mage and Argent Savant to do almost 1k damage a round with just magic missile, and pearls of power to keep the spell slots coming back. It was all the build can do, but it was very effective. It could even pass through a Broach of Shielding and the Shield spell. I've also used the various spell shaping abilities to turn sorcerers into AoE death machines, outdamaging a raging barbarian weretiger in hybrid form without nuking the party. Those were non-gestalt builds though.
EDIT: I just stumbled across this. Army of One Challenge
First, gestalt anything is horribly, horribly broken by default. Compared to some of the things I've seen done with it, you've just made a lovely Fighter 5.
Second, you answered your own question. With max optimization you can become a one trick pony that does an amount of direct damage that matters. Or... you can play a caster right out of the box, use save or dies instead, and be just as good, plus have many other tricks. And of course if you optimize the SoD caster...
It's essentially neutering yourself, removing everything that makes you awesome and turning you into yet another one trick pony, right along with the Fighter.
Pick a +2 LA race with a CHA bonus and no physical penalties.