In the center of Bangkok, near Platinum Mall, there is a hotel. The tallest hotel in Thailand, the Baiyoke II Sky Tower. At the top is a rotating viewing platform that you can go up to see a panorama of Bangkok. I took a camera up there and took a video of a loop around the Skytower. It takes about ten minutes to do the loop, so the video is at 2x speed so it's not so slow.
It cost me 220 baht, see the map below for where to find the tower, a ticket office is just outside the lobby and underneath the tower you'll find a market 'Indra Square' which is a great place for cheap clothes.
Nearest BTS is Chit Lom.