Some good programs nobody mentioned yet:
Irfanview (the best freeware image viewer I ever found)
Notepad2 (a very good open sourced replacement for the classic notepad, with many improvements without losing speed)
7-zip (a open sourced compressor which compress in the 7z format and is compatible with rar, zip and many others)
Virtua Win (with this program you can have more than 1 virtual desktop.. and is open sourced too
)
PDFcreator (creates PDF's
open source
)
StrokeIt (mouse gesture recognition engine)
