Beat-loggers index samples so we don't have to
It's no secret that the Internet is a safe-harbor for niche markets and small groups, but that doesn't mean some of them can't be extremely helpful in a pinch. Sample-spotting is one that has been incredibly helpful to us on numerous occasions.
More and more hip-hop is moving into the digital realm, with beats being made instead of sampled, but that doesn't mean drum breaks, synth loops and bass lines don't make a healthy appearance. If you've ever held a notion that you've heard a track before, you might find solace in websites like Hip Hop is Read, WhoSampled and The (Rap) Sample FAQ.
Even if you aren't a musician looking for mad beats and hot samples, these websites can often illuminate influences you might not have been aware of when listening to your favorite artists. Even more interesting is the themes that can be tracked through an artists career -- often times looking at these source materials is more interesting and comprehensive than any interview could ever be.
You can see what exactly Dr. Dre was listening to and utilizing on The Chronic, for instance, or you can see what RJD2 was pulling for Deadringer and why he ended up where he is now -- you can even watch as the Beastie Boys transgress from simple jazz breaks to more complicated rhythms.
It's a strong, vibrant community of people searching through catalogs of music and liner notes to find meaning in music. Hell, if nothing else, it'll get rid of that ear-itch when you're pretty positive you heard a Emerson Lake and Palmer keyboard solo in a song.