Fact: Youtube has the biggest database of community-driven song analysis.
There are millions (estimate) of rap artists with content on Youtube. This creates an amazing opportunity to mine this data for valuable information. Often, this’ll be in the form of User 1 asking what song is being sampled in the song and User 2 giving him the answer. Knowing this, we can search through videos to find samples here at www.rapmetrics.com/SAMPLE.php Simply enter the Youtube link and get the answers.
Here’s something I found out today with this little tool:
Relates these 4 songs:
The tool doesn’t work too well right now but with more focused keyword searching this could prove to be a powerful tool.
RapMETRICS 
Just try whosampled.com