Turn any wall into a whiteboard! This stuff is the bomb.
I haven’t used this brand before, but there are a few variants on the market. Once you get over your fear of writing directly on the wall, being able to write anywhere is very liberating.
At Lonely Planet, there was a team war-room where all the walls were painted with whiteboard paint. The kind we had wrote well, and erased well too. For a while, we had an entire business case sketched up on the wall and stakeholders could come and talk through the whole thing. We could change the slides right there on the wall, on the fly. A great place for thinking. Look out though, your wall is going to look like this in no time!
Here is another brand.
Special props to Nigel Dalton and Gus Balbontin on this one.