The best thing I have found is the "Zerogame" project by zerojay. And that goes for any platform. Basically, it's a bunch of old-skool emulators all rolled up into one application. Currently the following emulators are installed and these are the best ports for linux. (Based off of the Wahcade frontend)
Commodore 64
Gameboy
Gameboy Advance
Gameboy Color
Sega Genesis/MegaDrive
MAME
NES
SNES
Wonderswan
The project is currently in beta (latest release is 0.40) But a 1.0 release should come soon.
Here's the homepage
http://thezerogameproject.com/ But it's just an index page. Everything you need is in the readme which can be found here.
http://thezerogameproject.com/zerogamereadme.txt