An easy-to-use yet customizeable piece of software.
After testing many of the other options out there, I think Flip PDF is by far the best. It's easy-to-use, yet has lots of advanced options available should you choose to tweak it.
The output files are of great quality, and the page flipping animation is very smooth. The wizard is very simple, but has the drop-down boxes with advanced settings, which include everything from hardback simulation to page flipping speed to background images.
As long as you're not searching for a 3D page flip solution, this product is by far the best to choose.