I have an iPod touch which I have actually been carrying around for the past few months. There are very few applications that I really use that I couldn't just bookmark a webpage as I transition to the N900 but this is my list.

Facebook - covered with lite.facebook.com and that desktop widget as well as full FB chat interaction by Collabora.
Epicurious -is a great Recipe/shopping list manager that pulls from magazines like Gourmet and Bon Appetit
Fandango - Location aware and purchase movieticket with a few clicks
Airfoil Speakers - a remote speaker app for Airfoil enabling you to synchronize music across your wifi network. (there is linux source available)
mint.com - expense and money management
And then games
wordfu
bookworm