We have several here in San Diego. It all started (I think) with Taste of Thai. Now there are a bunch.

Katima - best Tom Ka soup
Bankok Spices - Tom Ka really spicy soup, my favorite for sticky rice with coconut ice cream.
Thai Time - wonderful Panang
Amarin Thai - intimate little place with lots of great food

But the grandmama of them all is Saffron Chicken. This started as a small take out place for Thai roasted chicken. They have expanded and grown quite a bit. The best in San Diego for salad rolls.

The best Thai food I ever had was behind Temple of Siam (my Thai friends booth at Ren Faires)
They took me (& a whole bunch of us Rennies) to Bangkok Thailand with them last December & the best Thai food I had there, was on the street or at the weekend market place.
I hated all the "Americanized" Thai Buffets!

Kauai has an exceptionally good Thai Restaurant in Kapaa called Sukhothai & I ate the freshest Green Papaya salad there almost everyday. Yum, so good!

Buena Park/Cypress has Bangkok Cafe, who has some excellent Curries, awesome Thai Tea, but no Green Papaya Salad much to my chagrine. Very good for "fast food!"

Long Beach has a couple of nice Thai eateries but "Signal Hill" (same strip mall as Turner's Outdoorsman & across the street from Costco) has the best for Thai Tea & Green Papaya Salad for that area!

In Seattle, I like Marlai on Sand Point Way

My all time favorite is Thep Phanom in SF on Fillmore and Waller. Also Basil on Folsom (if its still there).

Since I moved to LA, I haven't really found a favorite yet (Lanna Thai in Sherman Oaks so far, that is my regular place), but am looking forward to JitLada based on the response above.

Milford Massachusetts, Mango Thai Cuisine is a tiny homerun place. The guy who cooks loves to experiment. He has no english (and I have limited Thai) but hands out experimental dishes to see our expressions! 80% of what I have "experimented" has been awesome. His standard menu items are outstanding also. There is seating for 20 I think.

My Favorite Thai place outside of Detroit is in Canton, MI called Thai Bistro and in Madison Heights, MI is Bangkok Cuisine.

When in lovely Pittsburgh, visit : "The Green Mango noodle hut " in the regent square neighborhood on East Braddock avenue ...

OR

Bangkok Balcony on Forbes Avenue in the squirrel hill 'hood (both are in the east end of PGH . )

In Berkeley, California:

Thai Noodle has outstading kao soi
Lucky House has amazing curries of all flavor and an amazingly good pad kee mao
"Lao Thai" (technically in Solano) has the best red curries I've had outside of Thailand
Tuk Tuk Thai has tremendous (though slightly greasy) veggie dishes and a Tuk Tuk in the restaurant!
And of course, the Thai Buddhist Temple has all kinds of homemade goodies you can't get in any restaurant

In Boston: Brown Sugar (try their choo-chee veggie ham!)

My Thai teacher always liked to say (when asked which Thai restaurant she liked the best) that rather than talking about one restaraunt being better than others, you should assess which restaraunt is beter at each dish.

It is true, though, what has been said: Thai food is significantly better in Thailand...

In Seattle Rom Mai Thai on Capital Hill, not to meation that I can sit at home and a have my food food brought to me.
Im not sure how large there delivery area is here you go.
www.rommaithai.com/
good eats