Lethal Tactics is the main server i go on. It's a very popular server with friendly mods, helpful donators and a generally friendly atmosphere. It has no factions and no griefing ( so no worries, build something massive!) and is the basic SMP server. I'm usually around spawn, and when i'm done with my "massive project", i'll let newcomers live there until they get some resources.

the main server link on here is: http://www.planetminecraft.com/server/lethal-tactics/

server forums: http://www.lethaltactics.net/