I use it for a few things on a regular basis:
iCal pretty much keeps me on time (and in the right place) for all appointments/classes/lectures. Also keeps me from scheduling two events at the same time.
Contacts..well..self explanatory.
I spend about twenty minutes everyday reading FMLs on the FML app.
I use my iPod Touch as a remote to control powerpoint presentations. Also can use it as an external trackpad/keyboard as well as remote for: Quicktime, VLC Player, iTunes, and much more.
I play many games (Bloons, Pocket Tanks, Lemonade Tycoon). Makes train rides a lot faster.
If you are frequently in an area with a WiFi connection, internet access for Safari, Mail, AIM, facebook.