The Star Trek Reader I - James Blish,  Gene Roddenberry This day (Nov 22, 2008), I picked up all four volumes of Blish's adaptations of the "real" Star Trek's episodes for $20 (which I consider a bargain, so please don't comment on the mint-condition set you picked up at the swap meet for $2 :-)

I've never quite followed how Blish came to write these versions but in some cases they veered far from what found its way to the TV screen. Another thing I find attractive about this series is that Blish is a serious writer who gave some effort to making these stories good and readable.