Good tools are essential to good engineering... Recently I ran across a couple of good tools that will help with Framework design and implementation.
NDepends - is a tool that allows you to analyze your source code in order to get a grip on what is really going on so you can do large refractorings, reduce complexity, etc. Check out the online demos
SubMain also has a cool that is effectively like FXCop, but it automatically fixes the errors for you where possible. Check out this tutorial for more information..
What tools do you use everyday? anything else you think I should highlight?