I would recommend calling a glazier and mounting a sheet of tempered glass on the wall with small stainless standoffs. See http://picasaweb.google.com/spolsky/FogCreekSNewOffice#52853... for a picture. Looks great, not expensive, and cleans easily without ever leaving permanent smudges
In addition, the paint I had wasn't magnetic, which is a drawback as well, but there is magnetic paint, so you would have to think about two layers...
A more expensive version can be purchased through Behance: http://www.creativesoutfitter.com/Products/IdeaPaint/16?utm_... ($200 for 50 sq ft.)
""" FREQUENTLY ASKED QUESTIONS:
Q: Can the Dry Erase coating be used over a previous Dry Erase surface?
A: Not over an aged surface. Since this product dries to a very hard and glossy surface, the previous coating must be thoroughly sanded to remove the gloss """
As Louise's comment suggests, it's a little more difficult to erase.
http://www.kk.org/cooltools/archives/000679.php
I'm thinking of just using melamine on a wall. I might consider upgrading to Ceramisteel when I win the lottery, though. That stuff sounds amazing.