Have you ever tried to get some motion into your shots by panning with a moving subject?
Digital Photography School recently posted an article which included 5 tips for successful panning and provides some nice images as examples.
However if you want to take things a little further, have a look at the article on Harry Nowell Photography site on mastering advanced motion techniques. In the article they go beyond panning with your subject and talk about fixing your camera onto the moving object, such as a bike or car. Not for the faint of heart, or those with expensive equipment!