I have a Won Bros. pro-heat Titanium LCD II heater. Here is a link. Cheapest I have found them.
It has a sensor that goes into the tank anf gives a digital temperature read out on the display. I have it set at about 78 degrees. The digital read out says the temp is about 80. However I have a thermometer suction to the inside of the tank away from the heater and it reads 78. Pretty accurate.
I would go with a titanium because it won't break like a glass one will. If your glass heater breaks you'll have glass in the tank and and it may cuase an electrical surge in your tank.