My wife has a Betta, but since I'm the one taking care of it then I guess that makes it mine too. I must admit that it felt good to get that little guy out of his shot glass-sized dirty blue water cup and into a clean tank.
I keep my little guy (named Houdini) in a filtered 3 gallon tank. I had a heater in the tank, but the heater wasn't regulating like it should. I keep a thermometer in the tank, and it stays consistent at 78 degrees. No heater was needed. Living where I do, the weather outside rarely changes, so the temps in the house stay consistent as well.
I would keep a Betta in no less than a 3 gallon setup. Unless your temps are like mine, you do need a heater. I think a filter is needed as well. I got a 3 gallon starter kit from my LPS for $25 (cheaper than the "fancy" 1 gallon decorative bowl that had no filter). I bought the gravel for 5 bucks and added a live plant for $3. The Betta cost me $4. So for $36 total I have a great tank, a filter, gravel, a plant, a month supply of food, water conditioner, and a beautiful male Betta. To quote Martha Stewart, "It's A Good Thing".
Houdini got that name because he would often disappear behind the filter or the plant, then "magically" reappear. He loves swimming the length of the tank and responds to the sound of my voice. Great fish. I'm happy to give him a clean, happy and healthy home.
My 3 gallon tank for my Betta (Marineland Crescent 3 Gallon Aquarium System). I'll post pics of my tank and Betta soon.
This isn't a picture of my specific tank, just a picture from the stores website.