Jeremy Stretch has been extremely active in the CT3 wiki in last few days, writing about OSPF inter-area routing and various aspects of PIM. His articles cover the basics of PIM, principles of PIM dense mode, more detailed overview of PIM sparse mode and a hint what Bidirectional PIM is.
We've been discussing basic OSPF operations in the NIL forum. If you're aware of any good online resource explaining OSPF basics, SPF algorithm, the resulting SPF tree and the OSPF cost calculation, I would appreciate if you could post the link(s); preferably in the forum or as a comment to this post. If it turns out there's nothing really useful (which I doubt) I could write something, but I would rather spend time on more advanced (but probably less popular :) topics.