As long as your hammock is breathable, a ridged closed cell foam pad works great. I used to have condensation problems on cold nights, waking up in a puddle (wait! was that my sweat or did I just....) and then I realized the material of the hammock was not very breathable. I fixed that problem and now I only wake up in a puddle if I had too much tea before going to sleep.
I also found a great material called "Wipe Out". No not the show, but a flannel like material that is very wicking, very warm and very quick drying. On one bivouac I was laying in my hammock, watching WWII in HD, and spilled my green tea all in my lap. And yes, this time I know it was my tea since I was still awake. The temp outside was about 2deg and I thought,"Crap! This will never dry and I will be sleeping on ice". Never felt a thing! The tea had wicked to the outer layer of my hammock and, in the morning with the temps still in the single digits, the Wipe Out was dry. I was amazed! Great stuff!