h:panelGrid is the core JSF tag, and it allows organizing the View components in a 2-dimensional regular structure equivalent to the HTML table (which is what it renders as).
rich:dataGrid is an enhancement to this concept that melds the abilities of h:panelGrid and h:dataTable. Unlike the panelGrid, it binds a linear sequence of items (list model) to the view. Unlike the dataTable, it allows this sequence to be displayed in a 2-D array of cells, instead of in 1-Dimensional rows.
RichFaces is an open-source product of Red Hat/JBoss that supplies extensions to the core JSF tagset with enhanced abilities, including extensive AJAX support. I think you can find the details from the main
http://jboss.org webpage.
