Looks like a dahlia to me.

The leaf and flower both look like a Harlequin dahlia.

As the Fates would have it, I just posted photos of my Harlequin over the last few weeks to my blog. I've included the link below, you can compare them if you like. Your flower is incredibly reminiscent of the very first dahlia image on the very top post.

Here is a link that might be useful: Dahlia Images (plus other stuff, but...)

This post was edited by morpheuspa on Mon, Aug 11, 14 at 18:45

Thank you both so much and yes, morpeuspa, it looks exactly like your Harlequin!

You can lift and store the tuber over the winter if you like the plant, BTW. The little guys are no different from the large dahlia and store very well. The tubers are smaller and there are fewer of them, though.

They'll bloom even better the second year.

I believe it is 'Wheels'