Another look-alike for September Sun is Lunar Orbit (I think)

I second Lunar Orbit and September sun look-a-like too, I used to have them side by side.

Paul, you've read my mind with this thread subject. I've been thinking a lot about this very topic and two pair come to mind right away:

Lakeside Black Satin - Candy Dish
Dream Weaver - Thunderbolt

Gold Standard & Janet

Add Dancin' In The Rain to your Fire and Ice/Loyalist twins and make them triplets.

Other twins in my garden:

Paradise Joyce and Katheryn Lewis
Rainforest Sunrise and Little Sunspot
Heart and Soul and Wylde Green Cream (not sure on this one, but I have been told they are impossible to tell them apart. I have both and H&S seems to have slightly larger leaves, but it is growing in more shade so it could be the different conditions)

And isn't this one of the lists that Don R has?

Alexa

Nope, I don't have a list for this yet, it's on the "back burner" until next winter. :)

Paradigm, September Sun, Lunar Orbit, Polar Moon, and a few others very similar.

Polar Moon

Abiqua Drinking Gourd, Love Pat, Big Daddy similar, but ADG more deeply cupped.

Dancing in the Rain will get larger and more upright than Loyalist and Fire and Ice.

Dream Weaver, Dream Queen, Thunderbolt, and J.D.'s Luck very similar.

St. Paul, Pride and Joy, Lakeside Shoremaster, American Glory Be, and Pete's Passion all very similar, but not exactly identical.

Elegans and Grey Cole similar.

I have both Paradigm,and Polar Moon,and I bet if I put them side-by-side,and took away the name tags,you couldn't tell them apart. They are Identical to my eyes. Phil

Here's Dream Queen, Dream Weaver and Thunderbolt that Don mentioned. Adjustt for lighting and ....
{{gwi:1030916}}

Paul