Google Desktop Download
Google is my favorite Search Engine and they have some awesome tools. I have been using Google Desktop for several months and today they launch Version 2. This version is even better. I really like the desktop tool because there are so many times that I can't remember the name of a document that I wrote or read on my PC, but I can remember some of the content. I just type in a keyword and bam, there is a list of references on my machine that contain the word.
Now they have added some other awesome tools to it. A Sidebar that can display RSS Feeds, News, Stock Tracker, weather and more.
I have used Copernic as well, but I like Google.