I've been using copernic desktop for a while, since windows desktop search is pretty poor. Copernic is fast, indexes everything (emails, pics, etc., if you want). Anyhow, there are other options, copernic's just the one I've been using.
They're now running a mobile site that lets you do a copernic search of your desktop from your browser. Works perfectly on my touch pro, and is a huge bonus for me. Phone email client, for instance, will only hold a handful of messages, and lots of times I'm out and want to find a name or something from an email I sent 6 months ago.
I THINK there's a free version of copernic, tho I use the pay one. The mobile thing is free, will even work Windows Desktop Search if you don't want to use copernic.
http://www.copernic.com/
http://www.copernic.com/en/products/mobile/