This got a few retweets when I posted it on Twitter, so I thought it would be worth sharing here.
BFXR is a sound creator that you can use to create blips and bleeps and so on for games.
It has a ton of settings, most of which I don't understand, but if you just generally play about with it, you can create some great sounds. It has presets for explosions, bonuses, jumps and other gamey things. Once you have your sound the way you like it, you can 'export' it and download it as a WAV.
Yes, it looks like it comes from 1995 and who knows, maybe it does, but trust me it is a great tool.
Use it online at http://www.bfxr.net/ or download the standalone version.