Although there is nightlife entertainment all over the city in the form of pub's, restaurants and karaoke's the main strip of it is around the area with the big hotels (Pullman & Kosa). But the nightlife entertainment is very different as in other cities like Bangkok or Pattaya. Walking out of the Kosa Hotel to the left you enter a street with some small western oriented bars like "My Bar" and 'Eric's bar". There is also a Scandinavian bar serving reasonable good food like paste and pizza but of course also Scandinavian food. Continue walking on this street there are some very small street-stall bars opposite of the Pullman Hotel. They serve cocktails, beer and snacks. They are mostly frequented by Thai customers.
If you continue walking this street you end up at a T intersection and following the street on you left hand side you are passing many Thai style Pub's and Karaoke's. And also many small bars & restaurants, one of them serving good Thai & Western food. At the end of this street is on your left hand side a big open-air pub with life music. On your right hand side is "RAD complex", a kind of high-end style disco and entertainment complex with outside seating to warm-up and inside with live-music and Coyote Girls shows. Although I enjoyed the music here it is not my style.
So I went back to the Pullman Hotel and followed the street leading to the side of the building. Here are again some small bars, oriented for Western customers. Following this street, just behind the Pullman Hotel is a big kind of disco called "U-club" which seems to be THE place to go for the young Thai. There is DJ music and live music and a huge dance floor full of people. Drinks are not expensive. It starts to be busy around midnight and when I left at 3 it was all still in full swing. Be aware that it might be a bit difficult to find a TukTuk to bring you back to your hotel.
At the Kosa Hotel are of course also Karaoke and a full-service massage saloon. The once famous disco under the Charoen Thani Hotel is turned into a "7 days show" theater with too beautiful show girls. All not my cup of tea.
As my hotel was along "Bung Kaen Nakhorn" lake I walked every evening around the lake and found out that at the southern side of the lake is a 4-level office building with a very nice restaurant & bar on the roof-top called "Nice sky". They serve Thai food, beer and whiskey by the bottle or glass. Along the east side of the lake are many restaurants, small and big, simple and high-end style. Like "Smile along the lake" which is a modern high-end style restaurant serving great Thai food.