I'm pretty partial to Fluval's E-series. Supposedly the most accurate you can get shy of an external controller-based model (and some serious $$$), and they have an LCD temp readout on the unit instead of just a red "heating" indicator. I also like that they cycle more frequently with less heating per cycle (mind you, some people don't as it take longer to hit a temp, especially in larger FW tanks where there's less water circulation). In my book this just means temp changes are smoother (think more like acclimating) and less likely to cause undo stress on my livestock. Once up to temperature, I've never seen the tank budge more than .5 degrees from set temp. Mind you, I'm using a 50W model in a 9 gallon tank, but a friend's got the 100W in his 34 gallon basement tank and has had the same experience. Only qualified common gripe I've read about is that people may need to choose one size larger than their tank's gallonage would indicate.
I would imagine two of these backed up by a reef controller would be about as foolproof as you can get.
You'll have to get them online (last I looked Amazon had em for a song) or at Optimum Aquarium in order to get a sane price on them, but so far mine's been dead-on accurate (periodically verified with temp gun against rockwork).
