http://www.walrusphp.com/
They're going to release version 3.0 in the near future, which should also be more user-friendly, so you may want to wait a few days. However version 2.2 is quite nice so far and what I've been using. There's no server-side code in their script at all, so it's quite easy to get a handle on.
http://growth.smackjeeves.com