RocketDock - Mac-style program dock for Windows.
CCleaner - Cleans up Windows temp files, uninstalls, and scans registry for invalid keys.
XmlPad - I use this over Notepad++ for XML documents because it has built-in DTD checking.
FileMenu Tools - Great program for tweaking Windows Explorer.
Everything - Very quick index-based search for Windows.
Active@ ISO Burner - Free ISO burning utility.
avast! Antivirus - Free antivirus. I find it more responsive than AVG.