Buriram is about halfway between Surin and Khorat, and easily reached overland or by PB Air's (tel. 02326-8000; www.pbair.com) three weekly flights from the capital. It's the best base to visit Phanom Rung (daily 6am-6pm; admission 100B), a stunning Khmer ruin which was deserted in the late 13th century, rediscovered in 1935, and restored in the 1970s. This Khmer temple was built during the 11th century, and stands in a direct line between Angkor in Cambodia and Pimai, a little farther northwest. Like Pimai, it has benefited from a loving restoration by the Fine Arts Department, and is in some ways even more impressive than Pimai with its hilltop location and intricate carvings on the main prang (central tower). It's worth stopping by the visitor center (9am-4:30pm) to get an overview of the temple's most significant aspects.
An additional popular side trip from Surin is Khao Phra Viharn, another striking Khmer temple site, on the Cambodian border, with some wonderful lintel carvings, though not restored as meticulously as Pimai or Phanom Rung. However, at the time of this writing, it was closed to the public due to a border dispute, so check locally whether it has reopened before setting out on the long journey. When it is open, it costs around 400B to get in -- 200B each for the Thai and Cambodian authorities.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.