There's veiltail (the ones you most often see in stores), plakat, crowntail, halfmoon, double tail, dragon scale, giant and big-eared that I can think of
Check out the betta boys site, bettaboys.co.uk
I've never purchased from them myself, but I've heard plenty of possitive comments about them. They've got some stunners
You could take some filter media from your 10g (about 1/4) and that will cycle the 5g enough for one betta just saying. Then you don't neccessarily have to wait