Well, after searching for exactly that, this is what I found: It's called sfxr and it will generate 8-bit style sound effects either at random or from pre-set parameters, in modes for things such as lasers, jumps, explosions, coins etc. Unfortunately, it's official site is down at the moment, but it is luckily hosted on another site:
It's been posted before but who cares, I'm sure someone will download it who hasn't before.
Oh yeah, and the guy who made this also made a fantastic music making program called musagi. I use it all the time, it made the music for bombie zombie and sewah runs.
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