Okay, I got have only had my N900 for a few weeks. This is my list so far. These are the apps that I use daily,

Old friends that made the transition with me from the N810:
FBReader
MediaBox
Katana (On the N810, I used Rapier)
Mappero (On the 810, it was Maemo Mapper)
Xournal
Xterm
OpenVPN (To connect to the vpn at home)
VPNC (To connect to the vpn at work)
OMweather
mplayer/kmplayer
Free42
Fuelpad
Password Safe

New friends:
FM Transmitter/FM Boost
Conky
Catorize
Camera and BlessN900
SiB
Angry Birds
Stopish