I own
these speakers made by Cambridge Soundworks. They're only 4.1, but I don't know how much you'll really miss the additional channel. They also sell
these, but I haven't personally used them.
I can vouch for the high quality of the 4.1 set however, and I doubt the 5.1's will be worse. They're plenty loud enough, have an excellent signal:noise ratio, and have been going strong for four or five years now.