Among the rare photos I've taken this year using a "real" camera.
My DSLR isn't getting much play time at all, but the Sony F828, with it's infrared capabilities, still gets pulled out--at least in the winter and spring when the clouds do fun things here in SATX.
The use of a circular polarizer filter instead of one of the pair of ND4 filters that usually live on the end of it's lens resulted in the different level of contrast between cloud and background sky. The 1st photo features our neighbor's pecan tree, and was shot with the sun to my back. #2 (our sycamore) was pointed a bit closer to 90 degrees perpendicular to the sun's rays, resulting in a much more pronounced effect from the CP filter. End result is darker sky, whether shooting IR of color.
I prefer #2.
Out of them all, it's my opinion that #4 is the one most likely to end up as a print on someone's wall.