The [lampligher group][1] is a nice example, see e.g. the answer to [this question][2] by Jeremy Voltz, in which he wrote:

> The lamplighter group, defined as the wreath product $\mathbb Z/2\mathbb Z\wr \mathbb Z$, is amenable yet has exponential growth. It can be thought of as a bi-infinite sequence of street lamps, each of which can be turned on and off, and a lamplighter who moves along the sequence. The three generators of the group are to move the lamplighter right or left, and to switch the state of the lamp he is positioned in front of. With this picture in mind, it is easy to show the group has exponential growth.




  [1]: https://en.wikipedia.org/wiki/Lamplighter_group
  [2]: http://mathoverflow.net/questions/62302/examples-of-amenable-groups-other-than-z-n