I got the Reefkeeper Typhoon II. Its a five stage, one particulate filter, two carbon filters, a reverse osmosis filter, and a deionizing filter. This one also hase valves to flush the RO membrane with low pressure water and bypass the DI membrane for system flushing (supposed to help membranes last longer). They have three versions, all which appear to be the same basic system set-up with some different bells and whistles.
I am very pleased with my set up.
Good Luck,
-Christine
PS - The water tastes pretty good too!