Good Feats: Point-blank shot, Precise Shot, Far Shot, Rapid Shot, Shot on the Run, Weapon Focus. Specialization is free at 6th level, so make sure you take Weapon Focus in your chosen bow.
Good Psionic Feats: Fell Shot (makes ranged attack into a touch attack for 5 PP), Psionic Shot (adds 1d4 non-elemental damage to your arrow for 1 PP), Return Shot (Reflex save as Deflect Arrows plus can return fire an arrow as a move-equivalent action -- read the whole feat, with Deflect Arrows, your return attack bonus is equal to your total attack bonus plus your foe's total attack bonus!),
Other useful Feats: Speed of Thought, Psionic Charge, Up the Walls, Mental Leap, Sharpshooter (from S&F, gives +2 to hit any target with some cover; essentially takes 2 points of cover bonus away from target), Extend Power (making buffs last twice as long). Most of these are movement related, a must for good archers.
Powers:
0- Bolt, creates arrows
0- Burst, gain +10 move as free action
1- Call Weaponry, summon bows (up to +4!) and arrows
1- Lesser Metaphysical Weapon, grants +1 to weapon (not as useful at higher levels, but necessary at low levels)
1- Skate, not on the PsyWar power list, but it is listed as such in the power description. +0-30 move.
2- Animal Affinity, boost DEX like Cat's Grace
2- Combat Prescience, +2 insight bonus to all attacks
2- Vigilance, see even in magical darkness, albeit 10' limit
3- Metaphysical Weapon, +3 bow, +3 arrows
5- Graft Weapon, +1 unnamed bonus to hit and damage
Taking a few or all of these powers will make the PsyWar archer the equivalent of almost any other archer combination. While he has only a 2/3 BAB progression, he can more than compensate with his buffs and bonus feats. As an additional advantage, at 20th level, he can be dropped buck-naked into an encounter and in a few rounds generate his own weapons and ammunition, all at +3 or better.
Since the PsyWar can't afford all the suggested Feats, he should concentrate his powers on making up for lack of movement (Skate, Burst, Dimension Door, Levitation).
Hope that helps,
Greg
edit- I forgot Craft Psionic Arms & Armor. As a full-level caster (like a Bard, but unlike a Paladin or Ranger), he can make psionic weapons and armor, too. The above list of powers will cover most of the really cool ranged weapon enhancements.