|Merman by Know-Kname|
I've featured other merman imaginings here (see label below) but this one breaks the mould a bit with his 'regular guy' look and facial hair. Know Kname gets the sense of swimming movement quite well. He avoids the thorny issues of respiration and reproductive functions by clever angling and basically not showing anything.
See more of his work at Know-Kname's gallery at Deviant Art
(but you'll have to hunt out pieces anything like this)