MS have released two cool add-on utilities for Windows XP in recent weeks, one of which I've started using already, and one of which I hope to have a reason to use in the not too distant future!
SyncToy is a free powertoy for automating the copying, moving and synchronization of directories. Great for quickly automating backups, synching between multiple machines, etc. Long overdue, and delightfully simple to use.
RAW Image Thumbnailer and Viewer gives you the ability to work with RAW images from most Canon and Nikon digital cameras within Windows XP in the same way you work with JPEGs. Not much use with my current Ixus V, but might become useful if and when I get a dSLR :-)
I like freebies.