Another player in the TFS-to-Outlook space is Ekobit's TeamCompanion. Specifically, TeamCompanion integrates TFS workitems into Outlook, giving you the ability to work offline with workitems, integrate with desktop search, create new workitems from e-mails, attach e-mails to workitems easily, mailing workitems, etc. It supports Outlook 2003 and 2007 as well as TFS 2005 and 2008.
Unfortunately, I haven't played with either TeamCompanion or TXLooker at all, so I can't really go into depth with any sort of comparison between the two products. I particularly like the idea of TFS/Office integration because those are the 2 apps I spend nearly 75% of my working hours interacting with. It reminds me of a part in the Will Smith film "The Pursuit of Happyness" where he figures out if he doesn't hang up the phone between calls he can get an extra 8 minutes over the day to make sales calls. If I didn't have to spend so much time switching between TFS and Outlook, I'm sure I'd be more productive!
Do you use one or the other? What do you like and dislike about them? How would you improve them? What else would you like to see TFS integrated with?