This picture shows the difference between turbulent and laminar flow from a faucet. The left side of the picture shows the turbulent flow, and the right side shows the laminar flow. I chose this picture because I think that this is a nice visual representation of one of the most important fluid concepts. I also liked the quality of this picture, which shows to some extent the details of the flow.
The image is by Haukur Herbertsson in Flickr.