I spent a good while combing the internet for a way to neatly store my bike vertically in my small flat without drilling or damaging anything. Finding nothing I came up with a ridiculously simple solution. This barely counts as a project as it requires no assembly. Nonetheless it is as effective as any other vertical style bike rack.
All you need:
Stick / chock (hockey stick works perfectly as it is slightly wedge shape, and the length means you don't have to line your tyre up every time you store your bike)
Its surprisingly solid, I've knocked it with my bag a few times and its never fallen over. And the walls remain clean and undamaged.