CED2911 released a port of SMS Plus, an emulator for the Sega Master System and Game Gear consoles, for Xbox 360 systems to use with the Xell JTAG Hack (right now just available for Xenon/v1 360s).

From the readme/nfo:

Introduction:
SMS Plus is a freeware, open-source, portable emulator for the Sega Master System and Game Gear consoles.

Changelog:
v140909a: Fixed controller bug
v140909: Sound is now fully working greats to tmbinc
Back to menu with select key

http://blogfile.wata.fr/smsplus/smsplus_20090914a.zip

http://ced2911.wata.fr/

Next well be genesis (mega drive).