This photo (hi-res version) shows the vortex wake behind a small propeller plane. To learn more about this photo, visit Wing Vortex Wake.
For more on wing vortices, and the danger they can pose to small planes following large ones, see the US Centennial of Flight Commission's Wing Vortices and Wikipedia's Wingtip Vortices. For an illustrated study of the Boeing 747's wing vortices, see NASA's Boeing 747.