Chances are, if you're a genre fan born at some point in the last fifty years, you spent some time reading original novels (as well as comics) based on popular franchises, or still do. With a number of "expanded universes" currently in flux, like Star Wars, I was wondering what your favorite media tie-ins were, past and/or present.
My tastes have usually run towards the bigger franchises. As a kid, I followed both Marvel's licensed takes on Star Wars (which was pretty good, though even the great Carmine Infantino couldn't draw the Millennium Falcon for crap) and Star Trek (which was uniformly awful). A few years later, I got into Doctor Who in a big way, though since none of our local channels ran the show my only knowledge of the character came through the UK comic strips in Doctor Who Weekly (which were also my first contact with Dave Gibbons) and the Target novelizations, which were available in America through many comics shops and bookstore chains. (The novelizations should probably be discounted, though, since they were technically adaptations of the serials, and not original material — though the writers frequently took liberties with the limited budgets of the TV show.*)
After Doctor Who, my next big obsession was Star Trek, which was really hitting its stride in the early '80s, thanks to the original cast movies and the novels published by Pocket Books. The quality of these early books was highly inconsistent, with zero editorial oversight in terms of continuity, canon, timeframe, etc., and a lot of them were truly godawful. But there were some outstanding titles nevertheless, like Vonda N. McIntyre's The Entropy Effect, Greg Bear's Corona, Diane Duane's The Wounded Sky and My Enemy, My Ally, John M. Ford's The Final Reflection, and Janet Kagan's Uhura's Song. And McIntyre's novelizations were stellar, too — her adaptation of Search For Spock transforms a so-so story into a truly moving SF epic.
By the time I was in my mid-teens, I started losing interest in franchises and media tie-ins in favor of "real" SF, and decided that I wasn't going to read anything that didn't have a "Hugo Award Winner" on the cover or got reviewed in Locus. (Which was a shame, since I missed some winners from that period, like Ford's How Much For Just The Planet?.) Apart from the odd item here and there, like a short-lived series of novels based on Infocom games from the late '80s, I barely looked at media stuff until Timothy Zahn's Star Wars: Heir To The Empire in 1991. And while I enjoyed it — I was going through something of an '80s movie nostalgia phase at the time — I never warmed to it, either. I followed the series with mild interest, and then gave up on the EU somewhere between the horrible Dark Horse series Dark Empire and the first Kevin J. Anderson novel. But I'd actually started reading Star Trek again, particularly Peter David's books in the TNG setting — he had a solid grasp of those characters, I think, because they were oddly akin to the X-Men and other superhero teams he'd worked on. (Michael Chabon has made similar observations.)
I'd all but stopped reading media books back in the mid-'90s, probably because I wasn't following science fiction in general too closely by that point. For a while they were omnipresent, but it seems like the growth of YA fiction and the popularity of writers like Martin and Rowling who have blockbuster shows and movies based on their own books has eaten into their popularity. I'm kinda glad that they're still around, though. In the '80s and '90s, when there were just a handful of TV seasons and movies, it was great to have extra adventures on hand. Nowadays, when there's a ton of new, "canonical" adventures in those universes, and much of it is available at the click of a button, it's kinda nice to know that fans still enjoy reading those books.
* Though technically Douglas Adams' first two Hitchhikers novels were also media tie-ins as well, since they adapted material that had already as radio shows. Gaiman's Neverwhere is another example — it's a novelization of a BBC miniseries.
** No, I never could bring myself to read the TNG/X-Men crossover that was published later in the '90s.