Dinner cruises
Dinner cruises on the Chao Phraya river are a touristy (but fun) way of spotting floodlit temples while chowing down on seafood and watching Thai cultural performances. Most operate buffet-style and the quality of the food is so-so, but there's lots of it and it's not too spicy. Note that drinks and tips are usually not included in the listed prices below. Always make a reservation before heading out to the pier. There are many competing operators, most of them depart from River City pier next to the Si Phraya Express Boat pier. Major ones include:

Chao Phraya Princess, 723 Supakarn Building, Charoen Nakhorn Rd, ? +66-2-860-3700. Departure 7:30PM. Large operator with four modern air-conditioned boats seating up to 250 people. Departure from River City pier. 1300 baht.  
Loy Nava, 1367 Charoen Nakhorn Rd, ? +66-2-437-4932. Departure 6PM or 8:10PM daily. This dinner cruise heads out with 70-seater rice barges. Departure from Si Phraya pier (near River City), and there is a free pickup from most hotels. 1400 baht.  
Maeyanang, 183/59 Soi Chuchart-anusorn, Chaeng Watthana Rd, Nonthaburi, ? +66-2-659-9000. Departure 7PM daily. Catered and operated by the Oriental Hotel, the Maeyanang is a custom-built ornately carved teakwood boat seating only 32 people, small enough to venture off the river down the subsidiary klongs. Departure from Oriental pier. 2000 baht.  
Manohra, 257 Charoen Nakhorn Rd, ? +66-2-477-0770. Departure 7:30PM daily. These restored Thai rice barges seat 40 people. Departure from Marriott Resort pier, with an optional pick-up from Saphan Taksin BTS station. 1250-1990 baht.  
Wan Fah, 292 Rachawongse Rd, ? +66-2-222-8679. Departure 7PM daily. These two-hour dinner cruises include a set meal of farang-friendly Thai food and seafood, live music and Thai classical dancing. Departure from River City. 1000 baht.  
Yok Yor Marina, 885 Somdet Chao Phraya Soi 17, ? +66-2-863-0565. Departure 8PM. Operated by the famous seafood restaurant, this is a much more local (and cheaper) option than the tourist cruises: pay a 160 baht "boat fee" and then order off the menu at normal restaurant prices. Departure from Yok Yor Marina on the Thonburi side of the river. There is a free shuttle service from Saphan Taksin BTS station.