Baan Khanitha's largely frequented by tourists and hence their food, while not bad, is considerably toned down compared to the real thing. Not bad for a first taste of Thai food, but rather tasteless after two months in the city. =)
Personally, I'd say the best Thai food I've had so far was at Saffron, atop the Banyan Tree on Sathon Rd. It's quite expensive though (1000+ baht a head)... but it's also excellently located for a nightcup at the aptly named Vertigo Bar above.