As some members already know I just got back from a 4 month trip travelling through Thailand, Laos, Cambodia and Vietnam.
On this trip fishing wasn't a priority for me but I was able to get out a few times although only my first outing is really worth mentioning. This was to a place called Bungsamran fishing pond which is actually inside Bangkok's city limits. It isn't a cheap place to fish(especially because they doubled their foreigner rates since I was there...) costing you a good $100-130 per day with the new rates. That said I have never seen a fishing pond like this one and if you want to go somewhere and be pretty much guaranteed to catch large fish then this place should be on your list of places to go. In around 2.5-3 hrs I had caught the following and had 1 more get away right at the dock, and supposedly this was a slow day.
The first 3 are Pla Sawai (Striped Catfish) and the last one is a Pla Buek (Giant Mekong Catfish). Guestimated weights ranging from 20-40 lbs with the Mekong being the largest. The Mekong's can get up to 200+ lbs in this pond.
Needless to say it was a great day, I had planned on going there again before I flew back but since they had doubled their prices I decided not to bother.