Puki 3D

Flash game where you shoot albino vampire babies. Made to look like 3D, although it's not.

http://www.gskinner.com/games/puki/

Winterbells

A really well animated bunny wants to hop up into the sky, bouncing off bells the whole way, and you have to direct him. Game play is extremely simple - the rabbit follows the cursor - but still requires reflexes and concentration. The whole look of this game is beautiful and relaxing, and the music - which sounds a bit like the town music from Kingdom Hearts 1 - is appropriate, and not at all annoying, even when you sit here listening to it for an hour or so (which is about how long it will take to pry yourself away from this gem).

http://www.ferryhalim.com/orisinal/g3/bells.htm

Double Wires

A spiderman-type swing game.

http://onemorelevel.com/games3/double-wires.swf

Shoot The Sheep

Sort of addictive, but also very funny. Plus it's a fast game, the perfect break from typing out boring documents.

http://www.bbc.co.uk/science/humanbody/sleep/sheep/reaction_version5.swf