If you forgot your iPod at home, or are squeamish about file sharing, you can still listen to great digital music online simply by plugging in your headphones or turning up your speakers. Mercora.com is a hip peer-to-peer radio network composed almost entirely of music resident on people's computers. It's legal because you don't actually download the files.
The music is free, CD-quality, and like the illegal downloading sites, the collection is massive.
I'm a fan of the site because of its mission to uphold the letter and spirit of music copyright law by paying performance royalties to organizations that represent songwriters and music record labels. Everybody wins!
Mercora supports Internet Explorer version 6.0 and later and Mozilla Firefox version 1.03 and later. Works on PCs.