I've compiled a list of free graphics and sound files that you can use in your games. The chapter on using graphics and sound files with the Pygame library is in Chapter 19 of the "Invent with Python" book.

UPDATE: I just found a great, huge list: The Ultimate Indie Game Developer Resource List. There's also the Wikimedia Commons, OpenClipArt.org, and www.sxc.hu, a free stock photography site.

2D Graphics, Art, and Tiles

Sound Effects

Music

No Soap Radio - Free music organized for game genres.

Jamendo.com - Modern indie music released under Creative Commons

The Video Game Music Archive - Music from old video games. There may be copyright issues if you widely spread or sell your games with this content.

Public Domain 4 U - Old and new music that is in the public domain.

SimplytheBest Sounds - This site has both music and sound effects.

Useful Software