I wanted to create a list of the free (mostly) utilities that I use on a regular basis.  I've found that a lot of people don't seek out tools to make their lives easier.. strange.  This is not an exhaustive list, but it's a start.

Link Shell Extension
Create hard and symbolic links in windows
http://schinagl.priv.at/nt/hardlinkshellext/hardlinkshellext.html

Notepad++
Great general-purpose text editor
http://notepad-plus.sourceforge.net/

FastStone Capture *
One of the best screen capture apps out there. Simple and effective.
http://www.faststone.org

7zip
Best compression tool available
http://www.7-zip.org/download.html

Ditto
Great tool for keeping a clipboard history. Great for refactoring.
http://ditto-cp.sourceforge.net/

Virtual Clone Drive
Nice free ISO mounter - works in Windows 7
http://www.slysoft.com/en/virtual-clonedrive.html

XPath Visualizer
Nice tool for testing XPath expressions without the bloat of larger multiple-purpose XML tools
http://xpathvisualizer.codeplex.com/

XML Explorer
Nice light-weight tool for working with XML
http://xmlexplorer.codeplex.com/

SyncBackSE *
Great tool for filesystem synchronization, there is a free version
http://www.2brightsparks.com/downloads.html

GrepWin
Coming from a Unix world, I need my grep. Search and replace, fast.
http://tools.tortoisesvn.net/grepWin

Mozy Home
The only online backup service I trust. Currently hosting 300GB of my precious data.
http://mozy.com/

TortoiseSVN
The only SVN client for Windows that's worth mentioning.
http://tortoisesvn.net/

VisualSVN Server
Great SVN server that run as a Windows service. Takes the headache out of manual setup.
http://www.visualsvn.com/

Snippet Compiler
Great tool for testing expressions outside of an IDE
http://www.sliver.com/dotnet/SnippetCompiler/

Development Specific

LINQPad
Awesome LINQ tool and snippet compiler... awesome.
http://www.linqpad.net/

GhostDoc
Must-have tool for generating meaningful documentation stubs
http://submain.com/products/ghostdoc.aspx

Reflector
.Net assembly analyzer and disassembler
http://www.red-gate.com/products/reflector/

ReSharper *
Must-have tool for refactoring. Version 5 looks stellar.
http://www.jetbrains.com/resharper/

VisualSVN *
Must-have SVN integration with Visual Studio 2005+
http://www.visualsvn.com/

* - Not free but worth the purchase price.