There's a sticky thread at the top of the Roleplaying forum but it's become a little out of date and confused since the forum merger. You could always have a look down there and see if anything suits you.
IIRC, the most active RPSGs in game at the moment are The Corporation, Unity Vigil, The Militia, Nighthunters. There may be more and these may vary in how IC they get. Check them all out and swing by the Militia forums if you fancy taking a look (link in sig).
Good luck. 
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
Hello.
Looking for a few tips on SGs, that would suit an RP-light player. Light just means I don't do this all the time, and don't always take it that seriously, much preferring to chat over a beer on a rooftop than bickering with heroes, and chasing arch nemesis, and such...
I'm curious about both red and blue side, and possibly in between. I'm kind of hoping to avoid overly themed SGs, as I find that I rarely fit into Arachnos, or Longbow, or any other specific.
Any tips, greatly appreciated.
Mac