Thanks to everyone for the suggestions. Here is what I found.
Stacks: Very thin, and under cooked. More like sautéed onions than anything. Ive eaten here three times and the food and service is always underwhelming. You can do better at places like Parkway and Chutpah. I believe the attraction is its downtown location and the fact its glatt kosher.
15 ria: Very thin and not very crispy. The blue cheese sauce over them was good, but I think it would have been better on the side. They do have a bottomless bloody mary from 11 4 on Sunday for $11, so they got that going for them, which is nice.
King Street Blues: Very thin and very crispy too. This was the best of the super thin crowd. A half portion was huge and more than enough for 2 or 3. They have excellent homemade potato chips and when I asked for a couple to try, the waitress brought a whole bowl so of course I overtipped. They also had a good beef chili. Purists may not like it for the beans and lack of spice (menu discloses this), but you got a large cup for about $3 and the cornbread it came with was far, far better than what Hard Times gives you.
Diner in Adams Morgan: My favorite. Perhaps I shouldnt have used the word thin as these were far thicker than the others were (but still much thinner than Hard Times). They were a little greasy but the rings were thin in cross-section but a bit wide (like a heavy-duty rubber band) so they maintained 'ring' shape. The other three were more like strands in the bowl, even the crispy King Street Blues rings.
If anyone has had the rings at Diner and can suggest similar onion rings, my cholesterol is almost low enough now to try another round.