Here are your two best bets for temperature controllers...
Johnson A419ABC-1C 120/240V Single Stage Temperature Control - The
Ranco ETC-111000-000 Digital Temperature Controller - The Ranco ETC
These units are both single controllers. They only control one thing. Ranco also makes a dual controller, which could be used to control both a heater AND a fan, with separate setpoints...
Ranco ETC-211000-000: 2 Stage - The Ranco ETC Store
The links I've provided are for the unwired versions. Poke around the website and you'll find their wired versions, for more money. The wired versions at this website though, do not include making the temperature probe waterproof. If you look around the DrFosterSmith website, you'll find the Ranco controller (both single and dual stage) wired, with the probe already waterproofed.
I've been running the Johnson single stage unit for about 5 months now. Wish I'd done it sooner. Way better control over temperature, and less stress worrying about the bimetallic thermostat in my heater welding itself shut someday and frying the tank. These digital controllers are waaaaaay more reliable.
I bought the unwired version and wired it up myself using an appropriately sized extension cord to give me the inny and outty plugs. I then got some airline tubing of appropriate size (can't remember what it was) and filled the end with silicone. Then I stuffed the temperature probe into the tubing and goobered (technical term) more silicone in there until I had a watertight plug on the end. The other end of the tubing is open to air, but that's above the water level of my tank. I then stuffed the sensor into my HOB
skimmer outlet because that was a convenient place for me. Controller kicks heaters on at 78 and kicks them off at 79.
I have also put a clip on fan that blows across the top of the tank on a standard timer. It comes on about 3 hours after the lights come on, and goes off a about 3 hours after the lights go off. That seemed a cheaper route than going with a dual controller, and it seems to work. (Just PC
lighting, not halides... but my house doesn't have AC
and it can get warm.)