1. Keep track of all phone numbers and addresses (HotSync to MS Outlook).
2. Keep track of meetings, appointments, and anniversaries.
3. Read ebooks.
4. Play games (RPGs, chess, Taipan, Solitaire, Hangman, Scrabble, Bejeweled, Mah-jong)
5. Used to have Avantgo, but I only have 2MB of memory, so it had to go.
6. Convert measurements from English to English and English to metric (I found a program that does dozens of conversions - good for kitchen chemistry).
7. My friend uses hers (Sony Clie) as a TV remote control.
8. Travel Alarm Clock
If I had more memory, I'd probably have a lot more stuff in there.