I think that the above posts may have contradicted AMG's initial recommendation; congrats, guys!
I agree with all of the above, especially the suggestion that you start with the core books and Eberron only, and make everything else subject to DM approval. One exception: I think Power Attack is balanced
just fine in 3.5. It was a worthless option in 3.0, and actually gets used somewhat now. There are numerous mathematical analyses of how the feat actually works in 3.5 (including a PA optimization calculator) on these boards, if you'd care to search.
As to suspicious stuff in the core rules:
1) Druids + Natural Spell. This may in fact work just fine in most games, but I personally find the druid a tad strong for my tastes, and the combination of wild shape and spellcasting is especially problematic. I'd stand by and prepare to house rule this one: Two decent house rules I've heard of would be to give Natural Spell a +1 level adjustment (my rule, which may be a bit extreme), or to make it a metamagic feat that makes the spell prepared with it possible to cast
only when the druid is wild shaped. Or you could just use the AU greenbond...
2) Disjunction. Not overpowered or underpowered, just a mess to play. It's basically an extended middle finger to fighters, who not only automatically lose their buffs but also have a pretty good chance of losing their precious magic items (and fighters are equipment-dependent, after all). The fact that the spell has vastly dangerous consequences that almost never actually come into play just makes it that much more unwieldy.
3) Gate. If you find that you have crazy powergaming players, watch this one. 1000 xp seems like a lot, but for an ally with a CR 5 or 6 above the effective party level, it can make for an awfully cheap way to win battles. This is one that simply might not come into play, but then again...
My only calls. As to the ECSB, I still find the warforged + juggernaut combo and the Heir of Siberys slightly too powerful for my tastes (lack of healing really isn't a liability if there's an artificer or someone with a
wand of repair x damage in the party). The armor enhancements can be a slight problem too, but overall, I'd say you're good to go.