The current standings are as follows:
EKT - Elite Kamikaze Team - Run the popular marathon server and is very well known.
TmX - The Matrix Community - Run the popular AOW server and is also very well known.
The two of these are the biggest clans/communities that you see to this day. There are a few newer ones trying to get started.
JTeK - Currently running an AOW server, this is a smaller clan that I expect and hope to see gain more people as Renegade X gains popularity.
NrO - New Renegade Order - Also a new clan, started by the experienced clan administrator known as Hadeshots, is a professional looking site also promoting Rust and Clash of Clans.
WaRx - We are Renegade X - The newest clan, also sporting the professional appearence, specializes in skilled players that know what they're doing.
EKT - http://www.elitekamikazeteam.com/
TmX - http://www.thematrixren.net/
JTeK - (Sorry, I don't know the website if there is one, can somebody let me know?)
NrO - http://www.fireon-community.com/
WaRx - http://WaRx.boards.net/
These are the clans I've seen. I'm currently a member of TmX, and I hope I gave as much of an un-biased description of them as best I could. If anybody has any questions, concerns, or edits, please let me know!