I am starting out a new project that involves the use of JSF 2.0. From my initial reading, the Mojarra and Apache Implementation of the project covers the basic components that
There is one thing against Icefaces: a lot of components and functionality are only available in the Enterprise version, which is commercial, not free (but that might as well be a good thing since you get support etc. if your project can afford it).
Why not play with all three libs for a short time, build a simple project and see how you are getting along with either of them. My personal taste prefers Primefaces, but I haven't tried Richfaces since it turned JSF 2 ready.