I nominate
Limits by Larry Niven
It's available as a Mobipocket/Kindle or ePub from the publisher for $5.99:
http://www.phoenixpick.com/catalogue/PPickings.htm
(It was free in November 2012, so some members might already have it in their ebook collection.)
An excellent collection of Larry Niven's earlier work, first published in the mid 1980s. Fantasy and Science Fiction.