Hotel Nemrut
4 star hotel.
Zeus Hotel
4 star hotel.
Karadut Pension
+90 416 725 97 26 (ask for the Bayram (the owner))
30 TL/bed/night and includes breakfast
12 km from the top of the mountain, in a small village named Karadut
This is a really nice pension. The staff is very friendly and the food is excellent. Dinner 10 TL. There are great hikes you can do around the mountain side. Tour around the area + sunset at the top 50 TL per person. They will drive you up to Nemrut for 40 lira per car. Camping costs 5-10tl. Kitchen is usable. [Personal Experience: Owners pushed a bit to write good reviews, make advertisment and even to get on the street to talk to other travellers, besides from that they're nice and prices are reasonable.]
Plenty of accommodation, but don't trust the hotel managers. Ask around at different offices about the tours to Nemrut, and at the bus station about getting out of town once you're done.