We started a 'sticker wall' for Isaac, right next to his mattress. This 'wall' is actually the back of our wardrobe. First to go on the wall were the Cars stickers. Isaac would get up in the morning, and prone himself like that to look at his stickers on the wall.
By now, the sticker wall is quite filled - with stickers of Cars, Thomas the Engine, Spiderman and Barney & Friends. We're wondering where the twins' sticker walls would be... but guess we'd deal with that when we come to it :)