There are certainly a few around still although how active they are I can't say outside of my own.
The Militia has been running for over four years now and is a successful group of downbeat heroes who operate out of Kings Row. There's a number of mutants in there but we cover all bases. Feel free to come and have a look around our forums: www.themilitia.org.uk Our wiki entry is here for background info: http://union.virtueverse.com/index.php/Militia
We meet on Wednesday nights for teams, rp and TFs and on Thursdays for our sister villain group, The Cadre. There's general chatter on our channel and forum RP in between.
As for other hero groups, I think the Unity Vigil is still running and Nighthunters seems to be active. I'm not sure about anyone else. Have a look on the Union RP wiki (http://union.virtueverse.com/index.php/Main_Page) for a comprehensive list of all the groups but again, not sure how active they are. And you could also pop your head into the Union Roleplayers channel and see what the folks there can tell you.
Hope that helps but feel free to poke me in game on @Dante if you need any help. 
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
Actually, the Millitia looks like a good fit for the character I had in mind. Any chance of an invite or interview for 'Warrior Born'.
Sure, stick your head in the forums and say hello and give me a shout next time you see me online. Best way to get to know us (and for us to know you) is to come along with us on a Wednesday night and meet the team. Most of us have done RP from PnP to table top to MMOs so there's a fair spread of experience there. 
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
Hey all, just wondering if there are any decent roleplay based supergroups on this server for a hero that after milleniums of studying and watching the human race, has been forced into action defending the citizens of Paragon.
I'm an experienced Pen and Paper roleplayer but for some reason haven't got round to roleplaying in game yet. Anyhow, if anyone has any suggestions just gimme a shout here or ingame.
My globals @Dark Storm, for if ye wanting to conat me in game.