Bangkok is the center of Thailand's extensive bus and coach network, and virtually all provinces are reachable from here. There are 3 different bus stations located towards the edges of the city center.
The sprawling multi-level Mo Chit (หมอชิต, Tel: 02-936-2852) bus station is Bangkok's largest and handles all buses going to destinations in the North and North-Eastern regions, and most of the nearby central provinces too. Mo Chit is a somewhat intimidating place for a first time visitor with dozens of tickets booths selling tickets for their bus only, and this isn't helped by the fact that many have their destinations written only in Thai. However, as you soon as you enter you are very likely to be approached by English speaking touts who will ask you your destination and point you in the right direction. The touts here provide a generally useful service, as ticket prices are pretty standard and all companies operating within the station charge similar rates for a similar service so you are unlikely to be overcharged.
Mo Chit skytrain station, Kamphaeng Phet subway station and Chatuchak subway station are all relatively close to the Mo Chit bus station, but unfortunately none are within easy walking range so really the best way to reach the station is by taxi. All taxis will know where Mo Chit is, though some will know it as Mo Chit Song (หมอชิตสอง, "Mo Chit 2") or Mo Chit Mai (หมอชิตใหม่, "New Mo Chit") as the old bus terminal (also called Mo Chit) is located nearby.
The Sai Tai (สายใต้, Tel: 02-434-7192) station handles all the buses for destinations south of Bangkok, and so this is the place to come to if you're looking to get a bus to one of southern region's renowned islands or beaches. Although somewhat hectic at times, it's smaller, less busy and a bit more manageable than Mo Chit.
The Sai Tai station is on the opposite side of the river to much of the rest of Bangkok, and is nowhere near any skytrain or subway station. Quite a few public buses will end up on their routes round the city, but a taxi is the easiest and quickest way of getting there.
The Ekkamai (เอกมัย, Tel: 02-391-2504) bus station is by far the smallest, and handles the traffic for the eastern provinces and destinations. For tourists, it's of most interest for it's services to Pattaya, Rayong/Ko Samet, Trat/Ko Chang or Aranya Prathet/Cambodia. There is some overlap between the routes run from Ekkamai and Mo Chit - buses to Pattaya, for instance, will leave from both stations.
Getting to the Ekkamai station is very straightforward nowadays, as the BTS Skytrain Ekkamai station is right next to it (Sukhumvit soi 63). That is by far the best way to reach the station, as road traffic is often close to stationery along this stretch of Sukhumvit.
