I had bought a dinner plate bulb bag from Home Depot, and one of y dahlias just went into bloom. I think it's beautiful and would like to grow more but I don't know what it is
Best bet is to dig the tubers a week after a hard frost, and store them between 45-60 degrees so you can grow many more of that same type next year. (Research 'dividing and storing dahlia tubers' in the GardenWeb search function or on google for details on that)
The 'big box stores' typically buy from companies in Holland that aren't really concerned with correctly labeling in the first place, and when you buy an unlabeled bag, the chances of identifying the variety is not likely.
There a several thousands of named varieties out there, and plenty of unnamed seedlings floating around. Even when you think it is a match with another dahlia picture, it wouldn't be right to trade or sell those tubers with another grower under that assumed name without lots of experience in dahlias, and/or growing the actual variety next to your no ID plant and having an experienced dahlia person compare them for you.
You can give it a garden 'nickname,' but make it clear to folks you gift to that you don't know its actual name.
Enjoy it- it's very pretty!
It's beautiful whatever it is!!