I got mine from eBay, it was a really good bargain that way! I got the Drinkwell fountain, resesrvoir attachment and a pack of replacement filters, with shipping it was just under $40. The cats definitely love it, they drink waaay more water than they did out of bowls, and they're drinking from the faucets less too!
I agree with Mom of 10. I also got my Drinkwell on Ebay. I have had it for 1 year with no problems. My three cats love drinking out of the running water. In fact my 11 month old kitten takes a shower everytime she uses it, then wants to be petted. I would highly recommend it
The two main options seem to be the Drinkwell, which has a "waterfall" and a reservoir which must be bought separately, and the Fresh Flow (Petmate), which comes with a reservoir, but has a little ramp for the water to flow down. If your cats like to drink from the faucet, I'd go with the Drinkwell. If not, the Petmate should do just as well.