Terrarium Heater

what brand of heater would be best for a terrarium made of acrylic?
is that a water heater? i need one to heat from the outside. i keep tree frogs in the tank.
its a 90gal tank. 4ft by 2ft by 2.5 ft or so. 3/4 of the top is covered in a thin plastic to keep in heat/humidity, the rest is a screen. i have one tabletop light which we all know is very hot but i use it more so for just light during the day. also have a high uvb light on the screened side.