I use the following when I'm DMing:
* TableSmith: Random names, treasure, encounters, etc.
* OneNote: Campaign tracking, journal, notes, adventure info, etc.
* Excel: For tracking things OneNote can't, mainly stuff involving calculations (initiative/combat tracker, treasure tracker, etc.)
* Firefox: Mainly to access the DDI compendium when needed.
* Acrobat Reader: For reading gaming PDFs.
* Winamp: Background music
I've starting playing around with Masterplan and it's pretty impressive. Not quite perfect for what I want but most of the way there.
I was looking forward to the HP Slate as well (and the Microsoft Courier, which was also scrapped). I'm going to see what pans out in the tablet market later in the year (probably going with something Android-based).
Edit: Almost forgot - I've started using an external monitor as well (picked up a cheap, smaller LCD) to display pictures and info to the players. Masterplan lets you send screens to a second monitor, though so far I've just used FastStone Image Viewer to display monster pics downloaded from the WotC website. I have plans to use it for other player-oriented info as well, when I get time to set it up.