The often copied SR Laprade seatpost.

Adding a photo of what looks like an earlier model.  The clamp is a rough finish and the polished stem ends abruptly without the "V" shape depicted in the other photos.  Also, the fluted design appears to be a bit thinner and longer (maybe an illusion).  I date this to when I purchased it - 1977. 
It was in use well before that - or so I was told.  Single bolt was considered state-of-the-art for easy saddle adjustment.

Added two pics of a customized/"tuned" (approx. 15g lighter) version with a - imo manually - reworked polished head & clamp. The SR Laprade logos were removed and the edges between post and head were reduced to achieve an almost fluent passage.