Suvarnabhumi Airport to Southern Bus Terminal 
http://www.thai-experience.com/guide/bangkoks-two-airports/25/

http://wikitravel.org/en/Bangkok
also known as Sai Tai Mai, The terminal is scheduled to move to a new, even more remote location in Phutthamonthon Sai 1 in July 2007

Bus No.556 - Suvarnabhumi Airport to Southern Bus Terminal via Yommarat - Democracy Monument - Thammasat University - Pata Department Store - Southern Bus Terminal.

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Bus No.549 - Suvarnabhumi Airport to Minburi via Ladkrabang Road, taking a right turn to Rom Klao Road, cutting left to Sihaburanukit Road, taking left turn to Seri Thai Road. End the route at Bangkapi.

Bus No.550 - Suvarnabhumi Airport to Happy Land via Ladkrabang Road, On-Nut Road, turning right to Sri Nakarin Road, turning left to Ladprao Road and turning right to Happy Land.

Bus No.551 - Suvarnabhumi Airport to the Victory Monument via New Bangkok - Chonburi expressway to Srirat expressway for exit at Rama 9 toll gate to continue further along Asoke-Dindang Road and Rachawithi Road for the final stop at the Victory Monument.

Bus No.552 - Suvarnabhumi Airport to the On-Nut sky train station via Bangna-Bangpakong Road, taking a right turn to Sukhumvit Road until the On-Nut sky train station.

Bus No.553 - Suvarnabhumi Airport to Samut Prakan province via Ladkrabang Road, taking a left turn to Kingkaew Road, turning right to Bangna-Bangpakong Road, turning left to Sri Nakarin Road, turning right to Sukhumvit Road, turning left to Sai Luad Road until Samut Prakan.

Bus No.554 - Suvarnabhumi Airport to Don Muang Airport via New Bangkok-Chonburi expressway, turning right to the eastern ring road, taking a left turn to Ramintra Road, Changwattana Road, turning right to Vibhavadi Rangsit Road until reaching Don Muang Airport.

Bus No.555 - Suvarnabhumi Airport to Rangsit via Department of Employment - PTT Don - Muang - Vibhavadi Rangsit Junction - Rangsit.

Bus No.556 - Suvarnabhumi Airport to Southern Bus Terminal via Yommarat - Democracy Monument - Thammasat University - Pata Department Store - Southern Bus Terminal.

Bus No.557 - Suvarnabhumi Airport to Wongwien Yai via Rom Klao Junction - Chalarat Hospital9 - Technology Business Administration School, Samut Prakan - Chalarat Hospital 4 - Rung Chareon Market - Suksawat Road - Ratburata Hospital - Wat Sawetchat - Wongwien Yai.

Bus No.558 - Suvarnabhumi Airport to Central Rama 2 via Central Park Hospital - Chalarat Hospital 1 - Ramkamhaeng 2 Junction - Srinakarin Junction - Bang Na - Soi Lasan - Rung Chareon Market - Suksawat Road - Lotus Bang Na - Bang Pakaeo - Bhuthabucha Junction - Bang Mod Hospital - Central Rama 2.

Bus No.559 - Suvarnabhumi Airport to Future Park Rangsit via Dream World - Ek Prathum Hospital - Future Park Rangsit.

Bus Number 389 - Suvarnabhumi Airport - Pattaya
Bus Number 390 - Suvarnabhumi Airport - Talad Rong Kluea
Bus Number 825 - Suvarnabhumi Airport - NongKhai