The Panda Book of Horror
One of the most resilient Doctor Who characters has to be Iris Wildthyme: she's been in books, audios, short stories - and she's not even really from Doctor Who, sneaking in from Paul Magrs' proper books.
Despite all of that, I'd somehow managed to avoid her: I read a couple of her early appearances in the BBC Books and then didn't bump into her again. Until Obverse Books came into being, anyway.
Obverse is basically Paul and scourge of the forums Mr Stuart Douglas, set up to continue Iris' prose adventures whilst Big Finish take care of the audio side. If you've ever read a review on this site, you'll have seen Stuart's name as he's been nice enough to say some kind things about me over the years, so I thought the least I could do was get a copy of Iris Wildthyme and the Celestial Omnibus to support him.
What I wasn't expecting was to like the collection so much: it was one great story after another, and the more I got to know Iris, the more I realised I wanted to write for her. As soon as I'd put the book down, I gave Stuart a quick email, and the result is The Fag Hag From Hell - a drunken clatter down Canal Street in broken high-heels that you can buy along with all the other great writers' stories.

