Diggy's metropolis server
Mainly because it was so well designed, I loved the feel of everything.
That and organized crime.
As well as my first medieval builds using bot events.
Became popular for about a month or so.
The last thing I would have to say was all the SPACE rp's, the one with all the planets on the same map.
People would use the minijet or the Firebird to fly to each planet.