If you have hours to waste, and want something cool, try this:
In iTunes, enter the BPM for all your songs. Find a program to calculate it for you by tapping a button. Then, create a smart playlist that contains all the songs in a certain tempo range (90-100 or whatever). I tried, but didnt make it very far through my library entering BPMs. Smart Playlists are the greatest thing since sliced bread, though.