Time for another confession: I hate rpg fiction. I know hate is a strong word and I mean it in it's strongest definition here. Okay, why?
First, if you can't describe your material, without fiction leading into your setting book, module, whatever rpg splat book, you need to spend more time working on your ability to evoke emotional responses to your writing. Too often, I see this as a crutch used by weaker writers. I have read this in other people's products and rejected submissions sent to me due to it. My recommendation is to write the non-fiction first, then let that inspire you to write the fiction lead-in. If it does not inspire you to write something awesome, why would it inspire your readers?
Secondly, keep lead-in fiction minimal. If you can't do it in 2000 words in a core book or less than 800 words in a supplement, you have lost me. Give me a quick read, a taste, a sampling, and move on! I don't want 16 pages of fiction by various authors whose voices are so different to be jarring and turn me off.
Now, if you are butt hurt at this point, don't be. This is just my opinion. There are plenty of fans who love what you wrote. I simply am not your core audience.
As to fiction novel tie ins, I don't know that I can pick a fave. It's been too long. I will go with The Book of Cthulhu as edited by Ross E. Lockhart. It is not designed to be fiction tie in, but it is some of the best Mythos I have read.