First off, if you aren't familiar with the original Wasteland, published in 1988 for Apple II, C64 and PC and re-released again a couple of years back for Windows and what not as a sort of a remastered version, it could be smart to check out The Earth Transformed and Death Machines by Mike Stackpole and Nathan Long. While they omit quite a bit from the beginning of Wasteland, the two novellas are a re-telling of how Snake Vargas, Angie Deth, Hell Razor, Trasher and Ace along with Ghost (the narrator of the books) defeated the robot threat the first time around.
The two novellas are easy and fast to read and place a lot of emphasis on action. They do some amount of reflection on the human condition in the post-apocalyptic Arizona, but overall the plot revolves around the desert rangers just going from place to place, killing off the bad guys standing on their way. But if the original game is a bit too archaic on looks and gameplay, they are a decent way to get the basic gist of what happened in the final half of the game itself.
A bit more ambitious novel is Stephen Blackmoore's All Bad Things, which tells a tale of how two prospectors stumble upon an ancient TV-station a brimstone singing evangelist used to convey his version of the word of god to the masses. Samson, a bit thick but strong, and Curys, more sneaky and plotting, decide that finding the place is a sing from the god and that they need to bring the word of James King back to the sinner of California. And this is done best with a sword rather than reason.
All Bad Things is an interesting take on how people trying to find themselves rally behind a cause that looks nobler than it is. Samson wants to bring the god back to the people, but in the end, he has limited means on how do so and more often than not those means are just to bash in the brains of those who oppose the word of King James.
Out of the three novellas, All Bad things is the heaviest in subject matter. It's not just a background story of the religious sect of the game, it is a look at how religious fundamentalism can go to horrific extremes.
So, if novellas based on games are your thing, these are a pretty good choice. If you want 'em, you can get them at least from Smashwords:
All Bad Things
The Earth Transformed
I guess you can get them from inXile as well by buying the bit more expensive edition of the game.
The games are available as well from inXile or Steam or GOG.