There are two software I have on my Tablet PC that are "essential" in my list: MindJet MindManager for mind maps (it is "ink" enabled, and I have to post a review here sometime) and Microsoft OneNote.
With OneNote I don't have to carry a notepad with me to scribble, take notes, start projects and other stuff (yes, draw caricatures during meetings too). It works on "non ink" PCs as well, so if you want to have a look, try the OneNote Hosted Demo server.
There's nothing to install on your computer (perhaps an ActiveX to connect to the server). It simply opens a 15 minute session to a Terminal Server so you can try the software. It is really nice.
The second tip is the clean start.com start page. The start.com service is currently in beta, and the pages change quite a bit, but this one is an interesting start page, clean like the ones we love to use...
You can add RSS feeds, and more stuff - click on the Start.com logo on the top left and try it.
And the last one is the Search Results Clustering, a page that will great groups of results from within the search results retrieved. Interesting to see the topics related to each search performed.