I seem to have really good luck with sperm whales (Physeter macrocephalus).
At various times, I've found myself in the mouth of a sperm whale, photographing a sperm whale with a large chunk of giant squid in its mouth...and today, swimming for most of the day with groups of very friendly sperm whales.
It's been a really long day, and I don't have it in me to write much more, but as the saying goes...a picture is worth a thousand words:
Note: Photo taken under permit.