Free searchable database of hundreds of downloadable special effects and musical instrument samples. I have used this with my own kids for a few tasks and it has tens of thousands of useful audio samples.
Make no mistake Myna is Garageband in the Browser for mine is a far superior product to Soundation but nonetheless Soundation is another great tool for those want to get creative on the web and make some music with minimal fuss. Students and teachers can use this tools as a powerful online sequencer with 11 real time effects, 3 synthesizers, a drum machine and a fully integrated Sound Shop. It has both a free and paid version and is definitely worth a look if music is your thing. Get it here.