Oh thank you for posting that! In the past few days I have seen this flower blooming at several homes around the county and it is spectacular- your picture does not do justice to this flower. It is a really bright cadmium yellow.
I have been thinking of posting to see if anyone knew what it was.
The ones I have seen have been fairly large, 3'-4' high perhaps and so in diameter. This is just my guess from driving by.

Helianthus angustifolius - the native swamp sunflower. Typically blooms around here in mid to late October. In ideal conditions, it can get quite tall and is usually quite eye-catching.

Now I know what the two clumps that I have in my garden are! One is over six feet tall, and has been spectacular. The other patch is about 4 ft tall. They are just beautiful. Not sure if the cold weather predicted for the next couple of nights will do to them. Hope they last a while longer.

When I had Helianthus angustifolius I must have provided beyond excellent conditions with 9-10' plants. The flowers were glorious. BUT it spread like mad. Was finally able to kill it all. Now wish I'd moved some to the vacant land behind me.

Rosie, Sugar Hill

The Cannas to the right are about seven feet tall to give you an idea of size.

vroomp
Its beautiful! Whenever I see these plants at this time of year I just have to smile! Don't suppose you need anymore cannas to go with them do you :)

Those Cannas were removed from the compost pile since they refused to die. I removed two rather large Multiflora roses from that side of the yard ( they were actually trying to eat my neighbors house) and I had to put someting in there to fill in for the summer. It left me with an extra 600 square feet of sunny soil that needed some plants. I will probably leave them for a year or two but, I plan to install a cedar fence on that side and I didn't want to plant anything that I would have to move. Too bad all that rain beat the heck out of them.