Good luck with this one HCL.
Azurans (Human) from Magic of Incarnum, and the Goofy-Footed Halflings from wherever (i'm punting on the name),
get the Bonus Feat at first level like Humans do.
At level 10, this is an extra level 10 feat. At level 15 this is an extra level 15 feat ... effectively.
Most other races don't have scaling abilities, that work this well.
Early entry races, like Illumian Dual Spellcasters,
are worth an entire level of a PrC , and early.
Perhaps these are the most powerful races, in terms of keeping up the Spell Levels.
And since that's where the real action is ...
I've linked Obeah's Races thread over here, a couple of times. TO-ish stuff.
Cru did a Races thread recently ... and he posted (oops).
Senevri did Symbiotic template.
Tauric is silly, but fun.