I don't know if anyone's actually using my Reputation Tracker tool, but it now lets you select which sites you want to see reputation for.
For example, the URL for me to find out how I've done today on Stack Overflow and Meta is: http://csharpindepth.com/StackOverflow/ReputationTracker.aspx?user=22656&mode=today&sites=so,meta
Adjust for your own user ID.
I know the UI is somewhat crude — I wasn't sure whether to try to put the tables side-by-side or not.