Serious Eats - seriouseats.com

Here are a few of my favorite spots to eat Thai food in Bangkok, with the full range from five star hotel restaurant to a stall on the street:

Spices Market - in the Four Seasons Bangkok on Rajdamri Road, just a few minutes walk from the BTS Skytrain Rajdamri stop (right between the BTS station and the Erawan Shrine). Yes, it's in a hotel but it is also where Thais go for great (and yes, upscale) Thai food. The food is excellent, the atmosphere is upscale but relaxed, the service is great and (I think) it's still a good value overall. Try the yam pla duk fu--green mango salad with crispy fluffed fried catfish; the sea bass steamed with lime and chilies; and fried soft shelled crab with pepper sauce; I also love the pad kee mao, which is not on the menu but the kitchen will make for you (ask for the wide noodles).

Taling Pling-- http://www.thailandsbestrestaurants.com/restaurants/talingpling.html - Here you get yummy, affordable and authentic Thai food in a bright and slightly hip environment. There are at least two locations--the original on Thanon Pan near Wat India (this is the colloquial name of the temple); the second is in the atrium area of the Siam Paragon mall.

Chicken Soi Polo/Polo Fried Chicken - off of Wireless Road, down Soi Polo (amazing fried chicken and all kind of spicy thai salads); this used to be a hot sweaty alley stall, but they have expanded into the space next door which thankfully has air conditioning (if you don't reserve a table, you'll still be sweating it in the heat). Soi Polo is located just south of Lumpini Park and the alley entrance is next to the local police station.

Enjoy!