3. Internet Archive Live Music Archive
If you love listening to live music but don't want to get involved in file-sharing or tape-trading the Internet Archive Live Music Archive is a pretty remarkable project. Featuring thousands of shows from hundreds of trade-friendly artists, the LMA gives the listener the choice of downloading full concerts or listening to them in their browser. Some bands have a handful of shows and while others have hundreds.
The bands available via the site skew toward jam bands because most jam bands are OK with having their shows taped. That's not to say that other styles of music aren't represented; you'll find bootlegs from non-jam bands such as Godspeed You! Black Emperor, Death Cab For Cutie, and Maroon 5.
Even better, you're not just limited to mp3s when it comes to downloading; if you just need to have the recording in higher quality you'll find some shows available in .flac format.
2. Who Sampled
Be it the base of a hip-hop banger or a part of a dubstep freakout, samples play an important part in modern music. Today's artists can breathe new life into a song we already know or turn it into something we'd never dream of. Sometimes we want to know more about that process, whether it's finding out where a sample comes from or if a song has ever been sampled in the first place.
When it comes to finding out about samples, remixes, and covers there isn't a better resource out there than Who Sampled. More than just lists of text, the site provides links to listen to the sampled song in addition to time cues for where the sample appears or gives you the chance to compare the cover and original . Because of the way the site is set up you can approach a sample from either side; if you know that Lloyd's "I Want You" samples an '80s song but don't know which one you can look it up and see that it's built on Spandau Ballet's "True." If you want to know every song that's ever sampled "True" then search for that instead.
Either way, you'll learn something new and hear things for yourself without having to look up the tracks elsewhere.