Second Calf Creek, very nice place to visit. If you like scenic drives and don't mind a little graded county dirt in your TC, the Burr Trail/Notom loop is fantastic. The Hells Backbone route from Posey to Boulder and the start of the Burr trail would be a nice route.
A visit to Capitol Reef is always nice too.
If you like wildlife viewing and less crowded boondocking, leave Posey and head up on Griffin Top for a night. This time of year is excellent for seeing mule deer and elk in the meadows off the road up there around evening time - and it's a thousand times less crowded than Posey.
No shortage of indian rock art to be seen not far off the main routes too, if you are in to that sort of thing.
Tons more to see and do in the area, especially fishing. And Posey is just about the most crowded spot on the mountain, and not nearly the nicest either, if you don't mind a little dirt road, there are many, many nicer places to camp around there.
- Coyote