Google Desktop and Desktop Extreme
You're an idiot if you don't put both on your computer immediately. Can't believe I waited so long. Amazing. Turned my user profile, which I began on a Win2000 beta machine back in 1999 and have taken with me to every new machine since, into an easily accessed archive of gigantic proportions, even to include all emails. Every damn email and file, and everything in them is indexed, and every search I've tried is virtually instantaneous. Jesus, it even indexes everything you browse on the Internet, so when you search for something, you get results from your browser history. Don't be an idiot. Update: And with this, not only can you search all of your machines (I have 3: office, home, notebook) in one search, but you can search them all from any web browser on the net, from anywhere, and retrieve the results.