A lot of these tools were taken from Scott Hanselman's site hanselman.com, so check that out for more of these cool tools. These are just the ones I've found useful as well as others I've come across. Enjoy.
7-Zip, a free zip utility that's much faster then Windows Zip and much more free then WinZip.
FoxIt Reader, a free PDF reader.
Primo PDF Printer, a free PDF printer.
Virtual Clone Drive, a free tool that allows ISOs to be mounted as if from a DVD Rom.
Notepad++, a free editor that is a made to order replacement for Notepad.
ZoomIt, a free zoom tool, much better then Windows Magnifer and really useful for presentations showing code.
TaskSwitch, a really nice and free replacement for alt-tab.
CleanSourcesPlus, do you find sometimes in Visual Studio that cleaning the solution doesn't get rid of any files? Well with a right click on a folder this app will blow all that away!
CopySourceAsHtml, nice plug in for Vs2005 - copy as HTML so no lose of formatting. Great for documentation, forums or blogs.
CommandPromptHere, a few scripts to add the ability to go straight to a command window with VS tools loaded in a directory from right clicking a folder.
Lookout, an awesome indexed search tool for Outlook.
WSCF, Web Service Contract First - awesome tool for generating stubs for server and client side from WSDL.
Paint.Net, a free and much better alternative to MsPaint.
GhostDoc, quite nice for generating a framework on comments in C#.
CommandLineHere, some tools for adding a button to right clicking on a folder to bring a command line window to the current directory.
FileZilla, a greate FTP client.
Some other tools I'm currently trying...
SlickRun, a command line short cut for apps and web pages.
ProxyTrace, looks like a nice tool to see what SOAP is flying around.