These dahlias have stayed in the ground in my garden for several years and seem to be doing all right. Not sure what they're all called though.
http://s283.photobucket.com/albums/kk308/trinity_house/?action=view¤t=8967050a.pbw
Lovely- I've got a couple of dahlias which have overwintered well and plan to gt more!
Is the yellow/red one, Moonfire ? http://www.cmlb.net/ndcdwarf/Page.php?id=15
The bright pink one looks like Purple Gem http://www.cmlb.net/ndccactus/Page.php?id=14
Not sure about the others.
I always have a few dahlias which have over-wintered well and, every Spring I set small bedding dahlias from seed.
At the end of the season, they have produced small tubers and I leave them in the ground where many of them reappear the next Summer.
They're cheap, easy to grow and germinate within a few days and I like the bronze leaved variety, such as Diablo.