Gaming fiction has mostly been published by just a few companies:
-TSR/WOTC: TSR really got things going with the Dragonlance novels in the mid-80's. They took off and are still being published today. These were followed up with a series of Greyhawk novels which did not do as well, and then the Forgotten Realms novel line got going in 1987 and has never looked back. This was and presumably still is the heavy-hitter line of gaming fiction.
-White Wolf published numerous Vampire novels in the 90's and 00's though it seems to have petered out recently. I was never a Vampire player, so I admit to limited knowledge of these books and will probably not be reviewing them anytime soon, if ever.
- Games Workshop began publishing books set in their Warhammer and Warhammer 40,000 universes in the 90's and these have continued through today with new works published quarterly (if not monthly) and omnibus editions of older works coming out to keep them in print.
These are the major players as I see them at the current time