I’ve never been too terribly into post processing my photos, but there are so many nice iOS tools (way less overhead than firing up a beast like Photoshop) for doing post-processing now, and they’re really fun to use. I have about a half dozen little $0-$3 tools for doing fun things to pictures.
I always liked this picture, but I was never very happy with the color (the original was very much on the cool side, thanks to misconfigured white balance on the camera) or the DOF. I fixed the DOF with TiltShiftGen and took some wacky liberties with the tint in PS Express, both on the iPad.
The original, for comparison:
The universe is all a spin-off of the Big Bang.