Saturn Emulation has really come along way in the past year or so. Many of the emulators can now play several games and full or close to full speed. That being said, much work still needs to be done before Saturn emulation is a viable alternative to owning an original.
The following zip file contains the US, Jap, and Eur version of the Sega Saturn bios.
Download: Sega Saturn Bios Files
Saturnin is a great Saturn emulator. It has made great progress over the past year or so and several games are now playable! Runik has been working hard, and we see updates often on his work. This Saturn emulator is certainly one to keep an eye on.
Download: Saturnin .31
Satourne is another promising emulator for the Saturn. It shows nice results and is able to play some comercial games. The development of Satourne seems to have slowed down for the time being, but I do believe the project is still alive. Even so the author Fabien has helped alot of other authors out in there development. If work continues I think we will see great things from this emu.
Download: Satourne V1.1p
Partially Google Translated Page
SSF has been in development for a very long time. Perhaps the oldest Saturn emulator still in development. Little is known about this emulator as the homepage is not in English, but development continues and compatibility and performance is also improving. SSF requires a very up-to-date system to run, Recomending a 3.0Ghz processor, 1 gig of ram and a Radeon 9800 Pro video card for its latest version.
Download: SSF 007 Beta
Yabuse is a fairly new emulator to the Saturn scene. It was orignally written to run in linux but is now being ported to windows, Mac, and even Dreamcast! In the newest version several games are now booting up with even a few that are playable. This is certainly one to check out! You can find the builds for other OS's on the official website.
Download: Yabuse 0.50
No Saturn emulator would be without at least mentioning Cassini. Cassini is an emulator surounded by controversy and many ethical issues. It is based on the hacked comercial version of Giri Giri. No real improvements other than some Gui interfaces and what not have really been added to the original, and I don't think compatibility has really increased either. Due to the unkown legality of this emu, and the surrounding controversy I have chosen to not link to the homepage or provide a download. I strongly recomend you try out the above mentioned emus first.