Illithid Compulsion (prereq: Illithid Heritage) ups the DC for Telepathy (Compulsion) powers.
A debuff, as opposed to a buff: manifest Schism then have your schism-ed mind manifest Demoralize. Shaken status gives -2 to saves, and the power only affects enemies.
Power selection:
Charm - Good. Obviously use Psychic Reformation to swap it out when you reach Thrallherd 3.
Mindlink - Prereq., so you have no choice.
Crystal Shard - Good, but Crystalstorm is better. Also, see my notes on Psychic Scimitar.
Inertial Armor - Better to wait to take this one until higher levels, when you can augment it out the wazoo. As a Psion, armor doesn't cause your powers to fail. Get a mithril chain shirt ASAP and you won't even have to worry about not being proficient with it.
Vigor - Excellent power. Keep it. Love it.
Suggestion - Very good.
Psychic Scimitar - I really wanted to like this power when I read it, but it's a trap. While it looks like a versatile, PP-preserving, incorporeal creature-affecting, enemy-damaging version of Spectral Hand, its drawbacks make it unusable. It's got pitiful defenses and if it "dies" your most important stat takes a big hit. Furthermore, to get the most out of it you really have to focus on Touch-range powers. From Psion 1-4, I can only think of two that are worth it: Dissipating Touch and Empathic Transfer, Hostile. If you're using Psychic Scimitar then you're probably using C.Psi., which seriously nerfed the latter of those two powers. Then, on top of THAT, you really have to take Body Purification to offset the Int damage you're bound to suffer. It's just not worth it. BUT, if you insist on going this route, go whole hog. Drop Crystal Shard and pick up Dissipating Touch.
In terms of further suggestions, look up carnivore's guide. There's another thread over on the WotC boards about "the most powerful psionic power" by level. Regardless, remember that all such "guides" are somewhat subjective in their analyses. YMMV.