There are loads of rooftop bars in Bangkok. Right now, the Octave Rooftop Bar and Lounge is one of the favourites. On the 45th - 49th floors of the Marriott Hotel Sukhumvit you have great 360 degree views of the city. Being just outside the main tourist area, it often is a little less crowded than some other rooftop terraces, and you'll usually be able to get a table. Thanks to the glass balustrade you can see still see the millions of lights of Bangkok when seated. There is a DJ every weeknight and on weekends there are special acts.
Address: 45/F, Marriott Hotel Sukhumvit, 2 Sukhumvit Soi 57, Bangkok