The kosher book list I referred to earlier can be found here. What makes a secular book "kosher"?
For me this entails several things:
1) It should model good middos (character traits). Raising children is about lifting them up and modeling what it means to be a good person/Jew. Scoundrels, when they are clearly meant to be scoundrels, are fine. (There are some great scoundrels in Treasure Island, for example.) But if a lead character, often someone the reader is somewhat identifying with as we read the story, behaves rudely or obnoxiously to friends or (worse) his parents, it's not a book I care to read.
2) If a book glorifies another religion it's just not for us. I want our books to reinforce the middos we are teaching our children. References to holiday celebrations in, for example, Little House on the Prairie don't bother me at all. In fact, that's one series that really role models good middos!
3) If a book contains a lot of references to pop culture, it's not for us either - drugs, music, teenage dating, etc.
4) Not really to do with kosher, but twaddle is definitely out. The book must be well-written, the language rich, and the story well crafted. (This is especially true for our readalouds; I'm not quite as picky on what they pick up to read for fun around the house.)