I'm always really sad when I go to the pet store and I see all the Betta's just sitting there in cups that aren't large enough for them to even turn around - the water quality in those cups is often comparable to a sewer. In fact, it irritates me so much that I rarely even walk past the Betta cups anymore, because when I do I always have to fight the urge to save one, or two, or ten. But unfortunately, I don't have enough room for that many Betta tanks - especially since they really can't thrive when they're thrown into 1/2 gallon- 1 gallon tanks.
What most pet stores won't tell you is that a Betta actually thrives in a full fish tank set up - filtration, good aeration, the whole works. They may have long fins, but that doesn't mean they don't need clean water - if the filter is too strong for them wrap the end of a pair of panty hose around the bottom of the intake tube. And they may be able to breathe air at the surface if they need to, but again, that doesn't mean that they don't benefit from well-aerated water.
And you know what? There are certain species of fish that are compatible with your Betta so long as you have ample room in your tank, it doesn't have to live alone - just no fin nippers, gouramis, or other male Betta's (assuming you have a male). Females can live together, but not in anything less than 15-20 gallons, and you need at least three of them for the hierarchy to work.