If you've ever had an original Nintendo you have to check this out:

http://firenes.en.softonic.com/ (This is a download site in English)
http://www.firenes.com.ar/ (The manufacturer's site in Spanish)

You immediately can play over 2500 of the old Nintendo games. So far I've played Blades of Steel and RBI Baseball. I'm still trying to find that Nintendo Hockey game with the international teams and your choice of either the normal guy, the skinny dude or the fat guy.

For the guys my generation this is amazing nostalgia. My pitchers for RBI so far have been Jack Morris and Frank Tanana.