I've got a Callaway XR 4-wood, and I think right now it might have the most secure spot in the bag. Crazy long, very forgiving, and shallow enough to hit off the deck.
I would say any of the Great Big Bertha heads... I traded in my 3w and 3h and got the 5w.... i hit the 5w 10 yards longer than my old 3w.. it was an x2 hot 15 deg
Based on this thread, I just bought an XR Pro 4 wood! I posted the deal in the DOTD thread, but Callaway PreOwned is blowing them out on Amazon.com for cheap. I bought one listed as "good" condition for $56.