WXchick: You can't go wrong with the Hydor Theo heater that Adastra suggested and F&S aquatics is amazing. I'm a college student and have a 2.5 gallon heated betta tank on my desk. It can get to about 69 degrees in our room and the 25w Hydor Theo heater on the tank at a solid 80 degrees. And, I live in Florida. Tampa. So it gets hot outside but that means nothing for the fish tank in the cold room.
Betta fish always need a heater. If you just order everything you need from F&S aquatics then you won't have to worry about running around everywhere else. I just placed another order with them a couple days ago and when I run home for 2 weeks I'm picking up my package there. Excellent site, excellent quality.