BFXR is a slightly more complex version of SFXR, which was originally made at a game jam with the sole purpose of allowing quick and easy generation of game sound effects.

It can be used online (with flash player) or downloaded on PC or MAC for free. It is a really great little tool to get started, as it allows you to generate a random type of sound at a click of a button, like pickup/coin, lazers, jump, etc. You can then see and explore exactly what setting sliders go into making that sound, allowing you to tweak or make your own. You can then save and share these for others to edit, or export them as .wav files ready for use in your game.