I really like cork bark, its really light weight but the texture is great for them to climb on. Pepper can go up and down it at almost a 90deg angle. I also use branches (at least as wide around as the dragon is), slabs of rock and various other things. The important part is that it be easy enough for them to climb up and comfortable for the dragon to perch on. Personally I like solid things that hold heat better, vs hammocks and such.