Yosemite Valley Panorama
You've got to scroll around this image on the Original size. It's ridiculous all the neat little things you can see! I think my favorite part is the subtle area of light breaking through the clouds on the southern rim.
4 HDR images (+2/0/-2 EV each) taken in portrait orientation, stitched in PTGui, and tonemapped with Photomatix.
26 Megapixels at full resolution!