On my Milestone I use alot of these (should all be on Market) :

3banana (notes taking, kinda like Evernote with offline mode for Android)
Astrid (Task Manager, with sync with Remember The Milk)
Shopper's Paradise (Game, nice and addictive)
Aldiko (Ebook Reader)
Bloo (3rd party replacement for the official FB client, works WAY better...)
Loops (making musical loops!) (non-free, lite version available...)
Manga Droid (Reading manga...)
Exchanger (Currency exchange tool)
Hanping (Chinese <-> English Dictionary)