A few days ago NASA published the images taken by the STEREO mission probes, actually they are videos and some animations in 3D that are impressive if you see them with the required 3D glasses (you know, the ones with blue and red lenses).

But looking around I found a link in Isopixel to other impressive images of the sun.

This gallery of Space.com contains 15 images with a description of each phenomena shown in the images.