Well I work for NATS here "oop north" and I reckon ATCC is fantastic
If you follow the link of the xavius page to the extra sectors site (I think it's called Spongeys site or something) you can get a shed load more sectors, including a UK one
(Which is London Goles Sector) There is also an egroup called "atcc" that you may like to join.
I reccommend you give Sector 38 a try in ATCC first. It seems to be the easiest one for training and validation. That should get you used to the commands and the slightly strange procedures (strnage to me anyhow)
As for other sims there is one knocking around called TRACON but it's payware, unlike ATCC and quite hard to find. I've tried it and don't reckon it's anywhere nearly as good as the prog you have anyway!
Have fun and for all of my trusted collegues out there reading this - I know I'm sad - please don;t give me stick
Have fun anyhow
------------------
"Go around..I say again...go around"