Don't mean to butt in, but -
Check out
http://www.crutchfield.com/
Once you get past their annoying home page, they have a lot of good stuff. Even better - send for their catalog of car audio equipment. Everything from the most basic FM-only radio to super-duper AM/FM/cassette/CD/CD-RW/DVD/blahblahblah equipment. Even if you don't buy from them, the catalog has a wealth of information about what you can get, installation methods, and so forth.
Bill