Photographers use Star Filters sometimes to really make the highlights stand out, but if you do not have one you can use GIMP to reproduce the effect.
Star Filter Effect in GIMP
This photo manipulation is called a stereographic projection, which takes a standard photograph and stretches it around in a circle creating a Globe or Planet like image!
Planet Photo Manipulation in GIMP
When wanting to combine two or more photographs for a higher dynamic range (HDR) or correcting an overexposed photograph, I mostly use programs like Photomatix, however it is sometimes too difficult or frustrating fiddling with the settings for minutes getting nowhere. So, there is an easier way and in certain cases much better than an HDR especially if you want to avoid those really surreal photographs – Digital Blending is the way to go, you can be much more selective with your increases/decreases in dynamic range and get more realistic results.
Digital Blending - Petronas Towers, Malaysia
This is a very simple method to making photographs grungy, but its also a good technique to have handy in your mind for any post-processing you might do in the future!
The finished JPEG