If you're looking for some legit ways to download music for free on the web, here are some of the best resources to allow you download free legal mp3s.
From archive.org, this library contains over two hundred thousand free digital recordings (including Grateful Dead concerts), some available for streaming only, while others downloadable in mp3 format.
The etree.org community use this site for the sharing of live concert recordings by trade-friendly artists.
Amazon.com provides a large number of freely downloadable mp3s, available to anyone. Here's a list of all the mp3s currently available.
Miaminewtimes.com maintains a blog which highlights free new music to download every day.
Last.fm offers many mp3 downloads absolutely free of charge, with no registration required.