Unity is a powerful platform for developing 3d applications for the web, downloadable to the desktop, and for the iPhone. It's a complete development environment that allows scripting within an integrated 3d engine.
Here's a collection of fun games that have been developed using Unity.
Off-Road Velociraptor Safari
You're a Velociraptor wearing a pith helmet in a Jeep! Smash up the ones not blessed with your technolgy and drag them to portals to be turned into food.
Jetpack Brontosaurus
You're a Brontosaurus with a bike helmet and a big old jetpack! Fly around in space!
Minotaur China Shop
You're a Minataur who has finally saved up to buy his very own shop selling fine china. Get angry and smash it up!
Splume
Match colors with wobbly physics!
Tumbledrop
Don't let the star fall into the sea!
Avert Fate
Kill robots in generic-but-impressive first-person-shooter.
Tropical Paradise
Explore Far Cry-quality tropical island from your browser!
The Graveyard
Art game for serious people! (still, quite good in a serious sort of way)