Every day I realize how much I love Visual Studio for .NET development.... but, I believe that Resharper, may hold a value that surpasses Visual Studio's (I am using VS 2005 for WPF/WCF development).
I decided it would be great to compile a list of the most valuable tools for software development. These can be applications/plug-ins anything that you think holds GREAT value.
Also, please explain the benefits of the tool that you are posting.
Resharper:
Intergrated Unit testing
"Camel Hump" code auto completion
Find "usings" (inverse of "Go to Deceleration")
Code formating and member rearranging
Assembly and namespace inclusion (based on your code)
Check for common optimizations and possible bugs in code and suggests/rewrites the code for you (things like null checking, redundant delegate creation, inverting if statements, etc...);
Tells you when code and be more generic (may suggest things like "use this interface instead" if your code never refers to something specific on an object)
Helps you see code that is not being used and will clean any unused members.
File structure view helps you jump around the regions of your file (this is really awesome and clean).
Class searching (you can use things like camel humps) Asks you which partial file to open once you find a class.
It also has it's own plugin support, so you can do things like FxCop, documentation and relfector (all free).
This thing has so much I don't think I hit 10% of it yet :) [When I get time, I will try to add more... feel free to help me out]