here is my list of cool tetris games:

http://www.3dtris.de -- a 3d blockout tetris clone running in flash and thus in every browser

http://www.gravytris.de a cool windows tetris game in full 3d ( has a gravity gun - strange but cool)

http://www.blockout.net -- a blockout 3d tetris community, including a faithful remake of the original dos blockout from california dreams

http://www.tetrisconcept.com - the finest tetris community