Recently I visited a .NET dev team to take a look at design, code and processes with a view to making recommendations to improve delivery speed. One of the more minor, but easily generalisable areas is around tooling. I often find that the little extra tools you pick up can make your work significantly more efficient. Here are a few free ones I use:
A tabbed console which works well with classic windows shell and powershell. Good support for resizing, copy paste, etc.
.NET decompiler for those dlls that don't have source. There is also a great plugin that lets you decompile entire assemblies to files on disk.
When you're debugging SOAP or RESTful web services, Fiddler is great. It lets you see the messages sent / received and even change and impersonate them.
If you've got SQLExpress or just no tools installed, QueryExpress is a tiny (~100K) and quick query analyser style application for all breeds of MS SQLServer. Download in a few seconds, and be running queries before a minute is up.
Don't you hate it when Windows gets its locks in a mess and you can't delete/rename files? Unlocker will automatically pop up, show you which applications are holding file locks and let you release the locks.
A more powerful and accurate Task Manager application which allows you to see file locks and many other types of information.