I think that the yellow-bellied, or pelagic sea snake (Hydrophis platurus) is my favourite snake I've ever caught & photographed - because it looks so different with the fin-like tail; the fact it is apparently the second-most toxic snake on the planet; and how we had to charter a boat and convince the captain of what we were trying to do to get one!
Absolutely gorgeous creature - and apparently they also can't really swim - they just get carried on currents to get around!