MyMobiler (Free): Remote view/control your phone. Also comes with a file browser which allows you to install cabs remotely. Portable and very lightweight.
Astraware Sudoku (Free*): Fun time waster. * I downloaded this from the Microsoft link, which doesn't seem to mention that this is a trial copy or anything like that. While there is a commercial version, my copy hasn't expired (yet).
Midomi (Free): ID any music by singing/tapping or recording from speakers.
RemoteTracker (Free): Track, lock, wipe out your phone remotely if your phone is lost/stolen. Still trying experimenting with this, but it's the only free tool that does this kind of stuff
afaik.
Microsoft My Phone (Free and Commercial): Back up your phone address book, messages, pictures etc, making it easy to hard reset/migrate your phone, all for free. They are also offering location/wipe services, but these won't be free (a trial is available for now).
PocketIRC (Shareware): For you old schoolers out there, this is probably one of the better IRC clients out there. Doesn't expire as far as I know. Works great on my TP2.
QIK: Stream your TP2 video to the internet. It's a nice to have application, you never know when you need to document something live
KforTouchPro (Freeware): Allows you to use the physical keyboard with applications such as LogMeIn. Search the forums to find a link.
Google Maps (Freee): Definitely a must have, works well with GPS and cell tower triangulation.
LogMeIn.com (Free): Take full control over your PC. Requires the KforTouchPro software and
lmipie tool.
Rhodium Keyboard Controller (Free): Remap almost any button.