Legos are great, but if you're looking for something a little more animated, you might want to check out Cubelets, a robot construction kit that its creator likens to playing with bumblebees.
Yeah, I don't really get the bees reference either, but Cubelets look awesome nonetheless. Cubelets consist of a set of building blocks that you can interlock together to create a robot. Each cube has a name and a function that falls into one of three categories: action, sense, and think. For example, there is a block that acts as the battery, one that rotates, and another that provides light.
You can then combine the cubelets in a number of variations to create the robot of your dreams. That said, building your own robot isn't going to be cheap. Cubelets is currently available for pre-order through Modular Robotics, and a set of six Cubelets will set you back $160, while a set of 20 will cost you a whopping $520.
If you can't afford that, you can at least enjoy some free entertainment from the Cubelets promotional video below. Just watch. Trust me.