ReefKeeper64
Wanna be a reefkeeper
This is the only regulator to even look at:
http://www.aquariumplants.com/CarbonDoser_Electronic_Co2_Regulator_p/co2.htm
The rest will just be a waste of money, IMO.
+1 on the aquariumplants.com (AQ) electronic regulator. A TOTM winner local turned me on to these regulators a few months ago and he was right. AQ has the patent on their electronic regulator so you can't buy one like it elsewhere at any price. Pricewise, it isn't all that expensive either. One thing I especially like about my AQ electronic regulator is I can hear the electronic valve open each time it releases a bubble of CO2. It's only a faint sound but it is there. There is a also red status light that goes off telling you it is releasing a bubble as it works. Finally, my reactor has a traditional bubble chamber so that I can see the actual CO2 bubble escape and flow up through a chamber of water as it leaves the regulator and makes its way into my reactor. Once I put it all together I realized it is very easy to use. All in all, I know this regulator is absolutely reliable. It's like a digital Swiss made watch!