I've been AWOL from SOMD for some time, but when I saw this topic, I had to weigh-in. My wife and I lived in Thailand for three years, and we were delighted when Supon's became the first Thai resturant in the area. And after eating their several times, we think it's one of the best Thai resturants in the washington area.
I recommend the kanom jeep...which is an appitizer kind of like a dumpling. They also serve execellent Mussaman curry, which is a reagonal dish from southern Thailand that you don't often find at local Thai resturants. Their standard thai dishes, like Phat Thai and Tom Yum, are excellent too.
If you want to try a "authentic" spicy Thai dish, order the Phat Kee Mow...and ask them to prepare it, "bap thai-thai". Translated into English, Phat Kee Mow means, "Staggering Drunken Man's Noodles". It is supposed to be so spicey that you stagger like a drunk after eating it.
The next time I go to Suporn's, I'm going to order "Pla Chon Sam Roat," which is a delicious three-flavor Thai dish made with a fish that the US Government may soon ban. In English, "Pla Chon" is translated "Snakehead Fish" or sometimes, "Frankenfish". This fish has been portrayed as a threat to the environment, and possibly national security. Gale Norton, Secretary of One of Those Useless Departments, called it "Something out of a bad horror movie".There may have been a snakehead on the dinner table in a scene from "The Rocky Horror Picture Show", but some would argue that was a GOOD horror movie.
Snakeheads are FISH--they don't walk, breath air, or eat household pets. They do dig into the mud during dry spells, which is why they are also called "Mudfish". They taste great, and if you haven't tried one, do it soon before the government bans them. I hope Suporn's still has them.