Applications which utilise the accelerometer/G-Sensor built into the Touch Diamond:
GSen
BubbleLevel
Caver
Lightsaber
Kai's Bubble Level.Net
Lunar Tilt
Water Level / Spirit Level
Waterlevel
Diamond Profile Switcher
Diamond Shaker
Klaxon G Sensor Enabled Alarm Clock
Diamond TV supports landscape mode. Requires Gsen?
Sensor Maze
G-Invaders
Diamond Beer
Magic 8 Ball
Lunar Tilt
G-Flow
Black Box G Logger
Sensory Overload

Upcoming:
G-Sensor Calibrator (not working yet)
VueFlo (maybe... start with this thread for more info)
Touch Experience
Managers Sensors library for HTC Diamond - Following these threads One App Used As Plugins - or a Unified Architecture
G Pong

Ideas:
Game Controller also Wiimote
GPS Dead Reckoning
Auto Performance Meter / Dynamometer
Pedometer
Beer
Flow in Games
Alarm Clock
Marble Madness
Plane
Dice looks like GSmart has the app
Powerball
Maraccus
Pendulum
Snow Dome
Movement Sensor Alarm and some elaboration
Brick or Block not really very clear this idea - but hey, someone may get it!
Black Box G Logger
Psycho
G Mouse like Logitech Mx Air
Etch-a-Sketch
80'S Stripper Pen
Shake Stop Watch
Marble Madness port
Mercury not much info here
Tetris / Aquarium / Swimming Pool
Magic Money Machine as per Nokia N95
Crayon Physics

Other:
G-Sensor SDK
SDK Info
HTC Debug Tools

See this link for the updated list:
http://forum.xda-developers.com/showthread.php?t=411419