Shindola is a good guild that's not really pk-related but does a lot of small pk.
Overseers is another good guild, though I don't know how active they are.
Oblivion, my opinion is the same as Overseers.
Good luck in finding your guild.
Oblivion has level 30 base but virtually is inactive, with nobody ever online. OS was pretty active when I was in it, but I don't think they PvP at all.