Pic title: khaosan road (Link)
Bangkok is a large, sprawling city of course. It is technically split up into 50 different districts but these are rarely used in practice. The six major ones are noted here. This is helpful in finding hotels and making travel arrangements.
1. Sukhumvit — The long Sukhumvit Rd road, changing name to Ploenchit Rd and Rama I Rd going west, is Bangkok's modern commercial core, full of glitzy malls and hotels. The Skytrain intersection at Siam Square is the closest thing Bangkok has to a center. This makes a good meeting point as well for travellers. Most of the western-style hotels are around here as is good shopping.
2. Silom — To the south of Sukhumvit, the area around Silom Rd and Sathorn Rd is Thailand's sober financial center by day, but Bangkok's primary party district by night when quarters like the infamous Patpong come alive. Watch out for the lady-boys.
3. Rattanakosin — Between the river and Sukhumvit lies the densely packed "Old Bangkok", home to Bangkok's best-known wats (temples). Yaowarat (Chinatown) and sights around the Chao Phraya River are also included here. Bangkok's backpacker mecca Khao San Road and the surrounding district of Banglamphu are located on the northern part of this area.
4. Thonburi — The quieter west bank of the Chao Phraya River, with many small canals and some offbeat attractions. Not much around here unless you have a lot of time to spend wandering.
5. Phahonyothin — The area around Phahonyothin Road and Viphavadi Rangsit Road is best known for the Chatuchak Weekend Market and the old airport. There are some ratty hotels here - best to avoid them!
6. Ratchadaphisek — The district north of Sukhumvit centered around Ratchadaphisek Rd (aka Asoke) and reaching from Phetchaburi Rd to Lat Phrao. This area has really opened up recently as the new metro line follows Ratchadaphisek road.
Source: wikitravel.org - Used under Creative Commons License