On my xbox there are emulators for...
Master System / Gamegear
GBA / Game Boy Colour / Gameboy
Amiga (WinUAE-X and UAE-X)
(All with tons of games)
XBMC & XBMP (plays everything from divx to real media files)
Dongle free DVD player
A few homebrew games
Also there's 10 or 12 commercial games.
The XBOX is the most convienient way for me to run emulators. I turn it on, get presented with a menu and then choose what I want to run - simple as that - and as it's connected to a 32" TV and 5.1 surround system then it really is the dogs gonads!
The only issue I do have I yet to find the perfect screen size for some emulators - some just aren't quite right.