What really set Portal 2 apart from the first game was its clever use of gels, each providing new ways to zip around a level (and occasionally stump the player). And now you can own some of your very own.
OK, so this stuff won't make you run faster, jump higher or open portals on the floor, but the slime does come in little officially-licensed containers, are coloured appropriately and can even be shaped into forms you'd associate with their in-game behaviour.
You can buy one gel for $15, or get all three for $40.
Portal 2 Interactive Gels [ThinkGeek]