Jake of the Web

http://redruth.greenbean.org/~ben/4CR/smb_super_synth.swf

Or search 'mario brothers synthesizer'

A good looking, fun sound board that contains every song and sound from the original Super Mario Bros. It really took me back.

http://www.4colorrebellion.com/archives/2006/01/28/super-mario-bros-super-synth/

A downloadable version is also available, so you don't always need to be online.