One of my favorites is photo of a skeleton shrimp I took during the Belgian photography championship. It took me a lot of patience to first find a subject in a perfect position and then get the lighting right with almost no backscatter (no postprocessing allowed in the shoot-out). I probably spend more than an hour on this shot, but the result was certainly worth it!
Nikon D7000 and 105mm macro, backscatter miniflash and snoot, 1/320s @ f/32
The second one is a photo of a nudibranch (Polycera quadrilineata) on a hydroid (Tubularia indivisa). Both species are rather common around spring in the Eastern Scheldt (Netherlands), but I was very lucky to spot them together. Getting them both in focus and positioning the snoot was very challenging because I had very little space to maneuver. Even while nudibranches are not exactly fast moving, this nice composition didn't last very long. Sometimes you just have to lucky to be at the right place at the right time!
Nikon D7000 and 60mm macro, Sea & Sea YS-110 alpha with home made fiber optic snoot, 1/320s @ f/22