Google's ranking algorithm unveiled
As of today, Google has patented their ranking system. Know the gory details on this blog, or go to the source. Note that the patent specifies things that they may or may not have really implemented, but as generic guidelines can be useful.
Sorry to all of those who sticked to their official version ;)
The slashdot discussion on this is also interesting. And, for the sake of historic interest, everything started here.