Free shuttle bus from airport to go to the bus station where you can take a local bus to go downtown or around Bangkok.

Bus 550 to Happy land
Bus 549 to Minburi
Bus 517 to Hua Ta Khae train station
Bus 1 to Pattaya
Bus 2 to Nong Khai near Laos border
Bus 3 to Rayong, Chaataburi, trat
Bus 4 to Chonburi, Laemchabang
Bus 5 to Sakaeo