see:
www.wattspremier.com. I got the 5 stage reverse osmosis w/UV sanitizer. There are several systems shown on the website.
I paid about ~$300-$350, and it works well. I had the water tested by the NH DES (same people who test well water) and it passed easily.
They have pretty good customer service too. I had a leak in the spigot and called them up for a new o-ring for it. They told me the entire $40 part got recalled and if i gave them the S/N of the unit it may be covered under warranty, and i could get a free one. i couldn't provide the S/N (the system was in NH, i was in MA) so I just paid for it. A couple of weeks later i called them up with the S/N after i wrote it down and they credited me the price I paid...