This page is more information about friends although most of it is about guests:
Here are some of the guests that have appeared in friends:
Jean Claude Van Dam
James Michael Tyler
More names are yet to come!!!
Julia Roberts was one of the many guests in friends as an old school mate who wants revenge in The One With The Superbowl Part II.
Another friends guest:
Rachel's mmother was another guest in friends twice as well as her dad.