Of course they do! But be warned: heating a smaller (under 2.5 gallon) bowl without a proper lid is somewhat difficult. The bigger the tank is, the easier it is to heat.
I personally really like my marineland 10w heater. They sell them at petsmarts and cos as well as many other places. It works well and is reliable like most things marineland sells. If youre getting a heater, you need* a thermometer, too. They sell them everywhere, walmarts, even. Get one that has a suction cup.
Pay attention to wattage: I wouldnt go above 10w if you can avoid it.
Btw.....Tetra makes heaters, they sell them at walmarts....they suck! Haha. But thats my experience, though others often agree. Just a warnin' ;P