Sfxr is an inspiring little program which generates old-school sound effects for use in games or music, or whatever. It's one of those delightful little nuggets of software that just does exactly what it says it will and nothing more. It's great fun and looks great too, and its source-code fits in a single c++ file! Finally, it's cross platform, running on all the major desktops. Wonderful stuff.
http://www.ludumdare.com/compo/2007/12/13/sfxr-sound-effects-for-all/