For simple spot FX in animations, I found Tomas Petterson’s Sfxr to be a simple and powerful tool. It was written, in the author’s words, for those who “need some basic sound effects, don’t really care about top quality, have no idea where to get them.” Now there is a new version Bfxr which is even more fully-featured.
It’s simple to use, produces fun old-school sounds, and serves as a great introduction to electronic sound generation. I’ve always loved making electronic noise – my favourite tool for just mucking about was the Korg DS-10 cart, and before that I spent countless hours making my Gameboy SP splutter, glitch and hiss with the spartan beauty of Oliver Wittchow’s Nanoloop, which I now learn is available for iPhone and Android.
I have a fondness for 8-bit and glitchy old-school sound, having grown up with a computer that made no sound at all, and graduating to one that produced lots. I’m a sucker for anything (except the very experimental stuff) on the website 8bitpeoples.