I would like a good recommendation as well.
On my 4 days in Bangkok, I want to do a day trip to the River Kwai to see the war memorial.
Any info would be most welcome.
For the river Kwai you can catch the early train from Bkk noi station, I did this a couple of years ago, and when I got to Kanchanaburi I met a tour guide, he drove me round the sites on his side car, think I paid him 200-300b, check out Chungkai War cemetary, and the Jeath museum, you can walk across the bridge, and there are a few little restaurants by the river.
Can't recommend a agent, but there are plenty In town that organise daily bus tours there.