There are many interesting metrics, and most of them are easy to track. The number of classes, number of methods, and number of methods per class are all kept historically of course. Other metrics are source lines, story completion rate, tasks per story, and pair programming time versus reported defect rate.
There are lots of great metrics. Color charts and rates of change. Fantastic, and with a few scripts, a little Perl, some Excel, you could know so much.
Stop! Cut it out! Don't do that!
The success of your project is measured in Resources, Scope, Quality, and Time. Track these, as shown here, and you'll know more about your project than most teams ever do.
The success of your project is in your people. Watch these ...