Githyanki are ECL +2... the modifcations are:
STATS: Dex +2, Con +2, Wis -2
MotP - clairaudience/clairvoyance, dimension door, mage hand, and telekinesis, all three times a day at 16th level caster. Once you reach 8th level, you get plane shift once a day, also at 16th level caster.
In addition, you get spell resistence equal to 5 + 1 per character level.
PsiHbk - clairaudience/clairvoyance, dimension slide, and telekinesis, all three times a day. At 8th level, you also get plane shift once a day. All of these powers are manifested as a 16th level psion.
You also get the psionic attack and defense modes of mind thrust and empty mind three times a day.
In addition, you get power resistence equal to 5 + 1 per character level.
If your game includes psionics, I would suggest using the psihbk as the source, otherwise, use the manual of the planes.
Why? Basically because its in the race's history. They developed their own psychic power to overthrow the enslavement by the Ilithids.
Oh yeah, as far as skill bonuses and bonus feats, the Githyanki have none. If they did, it would be listed as a bonus feat, or as a racial skill bonus.
Anyway, this should be moot as soon as Savage Species hits the shelves. (I know the intent of Savage Species, not the content)