Eat
Bangkok boasts a stunning 50,000 places to eat; not only thousands of Thai restaurants, but a wide selection of world-class international cuisine too. Prices are generally high by Thai standards, but cheap by international standards; a good meal is unlikely to cost more than 300 baht, although there are a few restaurants (primarily in hotels) where you can easily spend 10 times this.
Sukhumvit by far has the best restaurants of Bangkok, though prices tend to be high. Practically every cuisine in the world is represented here, be it French, Lebanese, Mexican, Vietnamese, or fusion combining many of these together in a quirky, but delicious mix. Bangkok's Italian town is Soi Tonson near Siam Square. Of course, for those on a budget, street stalls abound with simple Thai dishes at around 30 baht. There are especially plenty of budget restaurants in Khao San Road.
There are plenty of vegetarian restaurants in the more tourist-friendly parts of town (especially in hippie district Khao San Road). Vegetarian dishes are also readily available on the menus of regular restaurants. On request, even typical street restaurants will easily cook a vegetarian equivalent of a popular Thai dish for you. Ask for "jay" food to leave the meat out of the dish. For example, "khao pad" is fried rice and "khao pad jay" is vegetarian fried rice. For vegans, the most common animal product used would be oyster sauce. To avoid it, say "mai ao naam man hoi". Be aware that all street noodle vendors use animal broth for noodle soup.
Street food
While not particularly high class, street food is among the most delicious food and can be found all over Bangkok - wherever you're staying, you rarely have to walk more than 100 meters for a cart of street restaurant. Many of street vendors sell satay (??????) with hot sauce for 5 to 10 baht a piece.
One of Thailand's national dishes you can try is pad thai (??????), stir-fried rice noodles with eggs, fish sauce, tamarind juice and red chilli pepper. It can be prepared for you on one of the ubiquitous carts, or in a street restaurant for about 50 baht. You can order it with chicken (kai) or shrimps (kung). Another one of Thailand's national dishes you should try is tom yam kung (?????????), a sour soup with prawns, lemongrass and galangal - beware, as it is very spicy! If you like sweets, try to find a kanom roti (????) street vendor. The crepe-like dessert is filled with sweetened condensed milk, lots of sugar, and can also have bananas inside. Also fun to watch them being made.
Khao San Road is known for its carts selling bugs - yes, insects. They are deep fried, nutritious and quite tasty with the soy sauce that is sprayed on them. Types available: scorpions, water beetles, grasshoppers, crickets, bamboo larvae, mealworms, and some more seasonal specialties. Break off the legs from grasshoppers and crickets or they will get stuck in your throat.
Ethnic cuisine
Thai dishes can roughly be categorized into central, northern, northeastern and southern cuisine. What's so great about Bangkok is that all these cuisines are present. Isaan food (from the northeast of Thailand) is a backpacker favorite; generally street restaurants serve on plenty of small plates that can be shared. Som tam (?????) is a salad made from shredded and pounded raw papaya - again, it is spicy, but oh so delicious. If you want to dine the Isaan way, also order some khao niew (sticky rice), kai yang (grilled chicken) and moo yang (grilled pork). Isaan food is very spicy; say mai pet or pet nit noy to tone it down. Southern Thai cuisine is also worth it; many of them have congregated around Wang Lang in Thonburi. At least try the massaman curry (??????????), it's delicious.
The place to go to for Chinese food is Yaowarat. It has a range of street stalls and cheap restaurants selling expensive delicacies at affordable prices - such as shark fin soup and bird's nest. Soi Phadung Dao is the best street for huge seafood restaurants. Try 1 kg of huge barbecued prawns for about 300 baht. Phahurat, Bangkok's Little India, has some decent Indian restaurants.