You will soon find a BPM database here. For more information about BPM (Beat Per Minute) please see here.

In the mean time, please have a look at these 2 nice ressources for BPM calculation:

• For MacOS X users, here is a Dashboard Widget made to fill the BPM field of iTunes. Tap the beat of the current track with your keyboard or your mouse, and the widget will compute the BPM and put it into iTunes. Then it's up to you to create some fancy smart-playlist using BPM (fast tracks for your running playlist and slow track for your romantic nights...) Download.
• For on the road users using an iPhone, here is a simple Web App that will compute the BPM you are tapping on your phone. Go here.