NES = Nestopia
*caveat; use the default color palette from FCEUX in place of Nestopia's own color palette if you want accurate colors: [url]http://www.fceux.com/web/home.html[/url]
SNES = bsnes
*caveat here; the longer bsnes development continues, the more features byuu strips from the compiled releases. It's at the point now where anything after v082 isn't worth looking at unless you want to start revising your SNES ROM collection into cartridge folders. If that sounds stupid it's because it is. But what are ya gonna do?
The emulator is otherwise awesome. If you want to use cores post v082 you can also try RetroArch with libretro cores:
Sega Genesis / Master System = Kega Fusion