Well, in general I suppose, I would suggest going with a Psion of any stripe, wearing the best armor and carrying the best shield you can afford. Equip him or her with a spiked gauntlet or similar weapon, to be used in the event of a grapple or something (and so he can make Attacks of Opportunity with some degree of competency).
You generally won't care about the armor check penalty to attack rolls due to lacking proficiency in the armor/shield; you'll be using psionic powers to strike at enemies, specifically any powers that don't require attack rolls. Take a few psionic powers to boost your Armor Class, but remember that an Armor bonus (such as from Inertial Armor, Ectoplasmic Armor, or whatever) won't stack with the armor you wear, so avoid that particular kind of power. Sometime around the middle levels (5th to 10th I suppose) get your armor enchanted to have the Ghost Touch property, to better protect you against Wraiths, Spectres, Ghosts, Shadows, and Allips.
I'd recommend a Kineticist, Shaper, or Telepath Psion, probably (in 3.0 the Kineticist is instead called a Savant). Choose a good variety of powers; don't focus on one sort (i.e. don't just take defensive powers, nor just offensive powers, nor just utility powers; pick one or two offensive powers of each power level, one or two defensive powers of each power level, and a few utility powers of each power level). Dorjes or the equivalent (I forget the 3.5 term, I think it was changed); effectively psionic wands or staffs, they can expand your effective number of power choices; try and get a hold of a few dorjes or whatever, but only with a few charges each (to avoid spending too much gold on them), whichever ones will help cover your weaknesses or any gaps in your powers (for instance, if you have no good mobility powers, a dorje of Fly, Levitate, or similar powers might be useful).
What edition of psionics are you using? 3.0 (Psionics Handbook, kind of a slim hardcover book), or 3.5 (Expanded Psionics Handbook, a thicker hardcover book)?