Pcsxbox is a port of the Playstation emulator PCSX to the Xbox. For most Xbox releases there is no download link due to XDK, so I gess you'll have to google around a bit.
Being myself a Linux man, here is a new version of Yabause, a Sega Saturn emulator under GNU GPL. It currently runs on GNU/Linux and is ported to Microsoft Windows and Mac OS X.
