There are few photographs that I find unconditionally great, but "Polar Bear and Reflection" by Paul Nicklen is one of these photos. For me, this picture comprises everything a great photograph should: It shows the subject in a new fashion, is perfectly framed and represents a clear, harmonic and minimalistic composition. The polar bear almost seems to float in the void and the bear's "cool" glance at the photographer and viewer is the icing on the cake!
Emphasizing one photograph of the huge body of work of Paul Nicklen may appear unjustified. But on the other hand, you may already have seen some of the extraordinary photographs of Paul Nicklen. He is famous for his extraordinary outdoor photographs of mostly polar regions. He has done numerous stories for National Geographic, including work on the atlantic salmon, the incredible leopard seal encounter or recently the spirit bear. Paul Nicklen has also published a wonderful coffee-table book entitled "POLAR OBSESSION", which everybody should buy (it only cost 29 USD at the moment!). Paul Nicklen uses his photography to rise awareness for the profound impact of the melting polar ice on these ecosystems and our planet as a whole. You may also want to read one or the other interview with Paul Nicklen (for example here, here, here, or here) or, much more impressive, watch Paul Nicklen's TED presentation below. It lasts almost 18 min, but it is absolutely worth your time. Enjoy!