Trackballs are great. They require very little desk space, since they are operated by scrolling a ball rather than the whole device. This means they can easily be used on your laptop. It will get in the way of typing, but this is a great way to surf the web when there’s limited space available, for example, while sitting in bed. After practice, you can even get away with playing an FPS like this.
The trackball in this picture is a brand new Logitech M570, courtesy of my sister.