Here is a robot that can climb walls reliably. The Geckobot has a motorized air suction system that allows it to walk vertically up and down smooth surfaces, such as glass, plastic, and whiteboards. As the name suggests, this robot mimics the movement of a real gecko, so two of its feet stay attached to the wall while the other two feet are lifted off of it.
When the tongue hits an object, the robot starts walking back down the wall. The Geckobot also moves it head and tail as it walks. You can find out more here.