Almost nothing. I've got one player a rogue, that wanted 'telling blow' as a feat, I reviewed it and allowed it for him, but none of my other players have asked for a feat or anything else from 3e, and I'm not volunteering anything.
I've got one player who wants to play a psionicist - and though the 3.5 psionics wasn't a bad version, I've hated psionics since 1e. I haven't allowed that, though with time I may, hopefully Paizo or a 3pp will do it justice, and I might then allow psionics once again.
I've been using Louis Porter Jr, and Rite Publishing new PF stuff wholesale, however. Though of LPJ's stuff, some of it seems 'broken'. I've got the entire 101 series from Rite Publishing: Feats 101, Magical Weapon Properties 101, and the 1st, 2nd and 3rd level 101 spells - so far.
I am digressing, but my basic answer to the OP, is practically nothing from 3.5 is allowed in my games. Makes things much simpler for me.
GP