While I've always been way more into reading than with TV, there are some shows I absolutely adore. Several of these I've picked up the mass-market paperback of and been less than impressed. For all CW drama fans, The O.C. was made into a novel series, fairly decent writing, good for the die-hards who love those little extra scenes. Also, Gilmore Girls has been made into novels, too, I'm pretty sure from Rory's POV, though I've never read them, just flipped through them whilst shopping.
As any original (before the TV show!) Gossip Girl fans know, there was a highly popular book series prior to the days when Blake Lively and Penn Badgley are being hailed as the next teen supercouple.
CSI, all its offspring, and several other crime shows (Criminal Minds and possibly Bones, though I can't be sure about that last one) have already been made into book series, written by TV-into-books superstar, Max Allen Collins.
Is there a TV show you think would be perfect as a book?
My top picks would probably be Lost and Numb3rs. I choose not to count The Numbers Behind Numb3rs or the hundreds of Lost guides, because they simply offer insight and no actual plotlines or extra info.