Isaan has four major border crossings into Laos, all of which issue Lao visas. The most popular of these is at Nong Khai, a route that provides easy road access to the Lao capital, Vientiane; the others are Nakhon Phanom, Mukdahan and Chong Mek. If you want to avoid possible queues at the border, you can get a Lao visa in advance from the consulate in the central Isaan town of Khon Kaen. Here you’ll also find a Vietnamese consulate issuing visas for Vietnam.
It’s also possible to travel overland between Isaan and Cambodia through two different border crossings: via the Thai town of Kap Choeng, in Surin province, to O’Smach, which has transport to Anlong Veng and then on to Siem Reap; and via Sa Ngam in the Phusing district of Si Saket province to Choam in Anlong Veng.