There are a total of six international checkpoints between Cambodia and Thailand:
1.) Aranyaprathet/Poipet which is the main checkpoint between the two countries and generally the one to use if going to Siem Reap from Bangkok and with improved roads in Cambodia is also suitable for Phnom Penh and really, any destination in Cambodia except the south coast. This border offers the most onward transportation options in both Thailand and Cambodia. This is also the busiest, most chaotic crossing.
2.) Hat Lek/Koh Kong a.k.a. Cham Yeam, is the southernmost crossing and best used for Sihanoukville and a more scenic route to Phnom Penh. While border guards tend to play games at all border crossings this is the place where, historically, you are most likely to be scammed for the highest visa and stamp fees.
3.) Chong Jom (Surin province)/O'Smach crossing, north of Siem Reap, west of Anlong Veng, useful for travel to/from Vientiane in Laos or Thailand's Isaan region.
4.) Chong Sa-ngam (Si Saket province)/Anlong Veng, also north of Siem Reap and useful for travel to/from Vientiane in Laos or Thailand's Isaan region.
5.) Ban Pakard (Chantaburi province)/Phsa Prom Pailin is on Cambodia's west side south of Poipet, north of Koh Kong and is a convenient entry point for travel to Battambang and also for travel from Thailand's east coast beaches such as Pattaya to anywhere in Cambodia. Connects with Chantaburi province (Pongnamron district), Thailand.
6.) Ban Laem/Daun Lem Border (Kamreang district of Battambang province) is also on Cambodia's west side south of Poipet, north of Koh Kong and is equally convenient as Ban Pakard/Pailin as it is just to the north of it. Also connects with Chantaburi province (Pongnamron district), Thailand.
http://talesofasia.com/cambodia-overland.htm
