There are tens AJAX frameworks available. I have noticed more RichFaces, OpenFaces and PrimeFaces.
RichFaces seems to be more used than others but what is currently missing is proper JSF 2.0 support.
My second choice of JSF 2.0 compatible frameworks was OpenFaces. Works fine but it is lacking some essential components like periodic updates.
Finally i found PrimeFaces, which has loads of components, and just works. Also PrimeFaces is tied into TouchFaces which helps you to build good mobile device UI-s