NCover may be worth a look. In my copious spare time. Code-coverage analysis could be a Good Thing ™ for test-driven development. (Apparently the people who wrote NCover thought so too.)
Actually, there are two apps out there that are both called NCover. One is on SourceForge and the other is on GotDotNet Workspaces. The SourceForge one has a sample report on their Web site (showing its own test coverage) that looks pretty tempting, but the GotDotNet one has Visual Studio integration. Both projects seem fairly active.
Here’s a post from the csUnit mailing list on how to use the GotDotNet NCover with csUnit.
If I ever get around to trying either one, I’ll post my experiences here. (Has anyone else tried either or both of them?)