The best I knew of are coolroms.com and freeroms.com. Of course, someone already mentioned Cherryroms.com. One problem with Freeroms is that even with a cable modem it still takes forever and a day to DL them.
The best site I know of to find some rarer NES roms is Marbysworld.com. Hope this helps. And btw, I know this sounds stupid, but I've found every GB rom I could EVER want except Kid Icarus: Of Myths and Monsters. If ANYONE has this or knows where to find it that's not a broken link, I'd greatly appreciate it.
