Mission for today : go check out Domestic.fr. They have candy for your walls - for your whole home actually. Design candy. Vinyl stickers, wall paintings, super cute porcelain plates, mirrors (like the fabulous one in the picture above) and more.
If I had a bigger flat with more free wall surface I might go for something like this (and if or whenI have kids I'll get them somtehing by Klaus Haapaniemi for their wall, like in the third picture below):