Back in the day before I knew how to do it all I used a guy called Mark Sherry - good service and affordable. His main music is trance but he does quite a few top level guys. he mastered some of my older progressive stuff fine.
Another I approached is Cid inc - I know he does a lot of mastering for popular progressive house labels.
Another guy is Glenn Morrison - you will need to pay top dollar for him though. Really friendly guy though and a bloody genius. He is the bloke with all the fancy outboard gear and what not.