After learning about JUnit, while learning to use OO in programing, I was delighted to find out about NUnit. NUnit allows you to test code with Unit testing to ensure code has not 'broken' after refactoring. The developers of NUnit did a wonderful job. However, there is a lot of functionality that is not in the GUI. If you are looking for more details, and a more 'professional' GUI, Zanebug may be helpful.
Zanebug is an advanced tool for comprehensive unit and integration testing. It provides full NUnit compatability, advanced testing features, comprehensive performance metrics and perfmon integration. It has guis for the perfmon and performance metrics that can be set up in the GUI. I do not, however, like the fact that you cannot save the tests selected as in the NUnit GUI. It refreshes and sets up all the tests to run each time.
You can find it here.