Digital sound effects can come in really handy for multimedia materials design projects and to inspire the imagination of our students.
Soundsnap is a really nice site which has a good size collection of free sound files. They are neatly catagorised and easy to search and you can preview them before you download them and most of them come in a variety of formats from wav, mp3, aiff.
You can register, but you don't need to.
Earlier this year I wrote a posting on my technology blog which looked at SoundTransit and I suggested a few teaching tips and ideas there, most of which would apply to these clips too.
See: Soundscapes from SoundTransit
Soundsnap is a really nicely designed user friendly site with a great collections of sounds.
Hope you enjoy these.