http://www.climateprediction.net/index.php

If you run your computer for long periods on end without using it (bro, mind, etc) you can use your spare mhz to do some calculus for the greater good...

Total Model Years - 18,679,047.078
Trickling Machines - 60,526
Completed HadSM3 Runs - 169,628
Completed Sulphur Cycle Runs - 13,537

...well, we all already knew it, but still:
http://www.sueddeutsche.de/kultur/artikel/631/90541/

A good bittorrent search engine... you can use all the search engines on one page
http://torrentscan.com/

Play all your favorite NES games online...
vNes
http://www.vnes.thatsanderskid.com/

This is a cool link if you find your self with your work PC, somewhere and want to watch some TV
http://www.tv-links.co.uk/