Tools that I use
A good developer is the one that finds the right tool for the right job. This is what my professor said to me on my third year. I guess he's right. My last year of studying was mostly about tools. In every situation we were forced to choose the right tool for the job. Let it be Mathematica for solving complex equations or PHP for producing a guestbook in 10 minutes. What tools you use, mostly define you as a programmer.
I believe that log4net is the tool that I use the most. It is a wonderful logging framework and I've never met something that would even get close to as useful. What I don't like about it is the complete silence when it doesn't work, when you have configured it wrong, which makes it quite hard to troubleshoot. A part from that, it is a great tool!
This testing framework seems to be almost a standard by now. I know there is MbUnit, xUnit and MSUnit, but I've never really found any reason to use them. NUnit just seems to be complete, especially now when it has ripped the RowTest feature from MbUnit ;)
I love this little mocking framework from Ayende. I really haven't tried to do mocking with EasyMock or NMock. String based mocking just scares me. The generic interface on Rhino Mocks is just genius and I can't wait to get my hands on version 3.5.
I don't think I would have gotten my hands dirty with revision control before I got my hands on this tool. It just makes it so easy and understandable. Now it is actually fun to check in/check outcode.
This tool makes it fun to do unittesting. "Run in debug" has saved my day IEnumerable times.
I have worked a lot with a CMS platform called EPiServer, and when you do programming with EPiServer you absolutely need this tool, because half of the exceptions that are thrown will be thrown from within the EPiServer framework. With reflector you can always dig right into the code and see what you did that the framework didn't like. Yay!
Let me just mention Notepad++ for easy editing of configuration files and Paint.NET for fast editing images/screenshots. I also use TrueCrypt for encrypting my source code when I'm out in the metro with my laptop. Launchy is a great tool for Windows XP when you need to start applications fast, and I would also like to mention Charles web debugging proxy when it comes to programming web services.