I have a Vivarium Electronics VE-200D with proportional control (a big selling point on the Herpstats as well) that seems to perform very well. Although for some set-ups a dual zone unit might work even better.

This is a piece of hardware that I honestly would suggest getting the best you can afford that meets your requirements (i.e. don't spring for a Herpstat 4/ VE-300X2 if you only plan on keeping a single pet).
Another thing to look into is the maximum wattage you expect to use and what the unit is rated for. Most manufactures are pretty generous in the max wattage area but, you definately do not want to exceed that rating. I prefer to keep it at or under 80% of the rated output.