MAKE magazine has just posted a short article mentioning the massive archive created for the OLPC (One Laptop Per Child) Project. The link in their article takes you to a 'wiki' post with a huge number of links to archived sounds in numerous zip files. (Many hosted at the Internet Archive.)
For example, this link should load a file I grabbed from there - beach sounds.
If you want to play with sounds there are a lot of programs available - many quite expensive - but one good one that is free is called 'Audacity'.
Justin Frankel, the creator of 'Winamp' (you can see the classic Winamp interface in the picture at the top) is involved in creating a new program, 'Reaper', which is almost a complete studio in a computer, although it won't be free as far as I know. The interesting thing as far as I'm concerned is the ability to share processing between computers connected on a local network.
You can view screenshots of the two programs here (Audacity) and here (Reaper).