There is a list of books with comicbook characters over here.
I actually liked Andrew Vacchs' Batman: The Ultimate Evil. The writing had a good modern noir feel to it, even though he did get on his soapbox regarding his main topic of crimes against children(a theme in virtually all of his writing). The story had Batman going up against a pedo-sex ring operating out of Gotham that sold kidnapped children to Third World brothels. Plus one of the more offbeat takes on Batman's origin that I've ever read.
C. J. Cherryh also wrote a decent Superman novel called simply Lois and Clark, although it was based on the ABC series Lois and Clark, not the actual Superman comic. Set during their engagement during season 3, before all the shark-jumping.
Not a superhero novel, although a superhero's origin makes up an entire chapter, there's always Michael Chabon's The Amazing Adventures of Kavilier and Clay.
Intellect and Romance over Brute Force and Cynicism!
After the Golden Age
Black and White by Kessler
The Chronicles of Silverwolf." If you're interested, take a look. You can read the excerpt here before you decide to order yourself a copy. So far I've had a lot of good reviews on it.
I think the reasons is that much like Star Wars if we turn comic book characters into novels or novellas then would they follow, compliment, be independent, or just an extension of their comic book counter parts.
I've read a Wonder Woman Novel, X-men, and Spiderman and for the most part they stand alone. a fan of the character might pick it up, but they largely stand alone and have no influence on their counterparts (No Pity in the Marvel universe). Or they are just print versions of graphic novels which means more money for the same or a slightly altered story
As for Original print there is a pretty good bit of material out there just spend an hour hunting.
The Damned Busters only a few bucks for the Kindle addition
There seem to me to be a fair number of such novels, whether they relate to comic book heroes or deal with original characters.
While not a comic book super hero, Gregg Taylor's "Tales of the Red Panda" novels are firmly set within the continuity of his "Red Panda Adventures" audio drama series. Taylor himself has written every episode (81 to date) of the series plus all three novels. Each novel can be enjoyed on its own, and so can the audio drama, but events of one are sometimes mentioned in the other, adding to the experience for fans. Whether you listen to the series or not, I highly recommend the novels for fans of classic pulps and super heroes. (Of course, I also highly recommend the audio drama.)
Matt Forbeck's Brave New World: Revolution just went live for sale yesterday.
Folks that backed the Kickstarter got it a little early, but now it is available for everyone. It is based on the dystopian heroes RPG that Forbeck created years ago Brave New World. Revolution is the first in a trilogy and a fun read, well worth checking out if you get the chance.
They are quite a few comics to books made. The reason we saw the novel as a medium get made into more graphic novels is because people get more money than transferring comic books to novels.
There are alot books fans who would gobble up a graphic novel because they are starving for more their series.
This isn't exactly a super hero book, but Bitter Seeds by Ian Tregillis gave off a comic book vibe.
From the Bitter Seeds website: Raybould Marsh is a British secret agent in the early days of the Second World War, haunted by something strange he saw on a mission during the Spanish Civil War: a German woman with wires going into her head who looked at him as if she knew him.
When the Nazis start running missions with people who have unnatural abilities—a woman who can turn invisible, a man who can walk through walls, and the woman Marsh saw in Spain who can use her knowledge of the future to twist the present—Marsh is the man who has to face them. He rallies the secret warlocks of Britain to hold the impending invasion at bay. But magic always exacts a price. Eventually, the sacrifice necessary to defeat the enemy will be as terrible as outright loss would be.