Camping at Pang Sida is in the same forest complex as Khao Yai, but much quieter, and a bit more difficult to reach. There is at least one good campsite in the park, and some great views and nature trails looking back towards Khao Yai and Thap Lan. I have not tried any of the trails, but there does seem to be an effort to signpost them. Probably the easiest way to reach pang sida from Bangkok is from Sa Kaew province to the south. This is well worth considering if you can only get away at weekends, and do not fancy sharing your campsite with your neighbours from Bangkok. The main viewpoint is definitely worth a visit both morning and evening, It is around 8 Km up the road from the camp headquarters campsite.
Camping at pang sida is a great alternative to Khao Yai, and seems to attract a slightly more laid back crowd than the weekend hordes from Bangkok found at Khao Yai, though the only campsite I know of in Pang Sida is really nothing special as it is in a bit of a hollow next to the road.