Kind of depends on how much you want to spend I'd imagine. Just browsing Petco's website, I found this Aqueon LED Aquarium kit
. It comes in 2 gallons, 4 gallons, and 8 gallons, but they start at $50 a pop.
I have never used it myself though, so I can't really vouch for quality. It seems like it comes stocked with a lot of the basic stuff you need other than a heater.
I have seen some people use Critter Keepers (which, admittedly, would be very cheap), but I'm not sure how well they'd do with a heater? It seems like they would be hard to get a heater to fit into as far as where the wire and such would go unless you cut a hole in the lid. I'd almost always go for a an actual tank if I had the option though.
I also saw a gorgeous betta at Petco today as well xD I was very upset my 5 gal wasn't ready for him, lol. He was one of the more active ones of the batch too.