I have one site for rom hacks. And I'm NOT giving it out. It's mine.. my only... my precccioussss.
As for roms, I have this one for MAME:
http://mamefans.metropoliglobal.com/roms.htm
It's all in Spanish, so I can't understand anything beyond the game titles. I don't even know what version MAME is anymore (after MAME.Net pussied out and took their roms down, I really stopped paying attention).