Start with the bestsellers. Even though a book's bestseller status doesn't guarantee its quality, looking at the top selling Christian novels does give you an accurate idea of what's out there. You can cross reference book on the New York Times Bestseller list with Christian book lists to find Christian bestsellers such as Frank Peretti's "The Oath." Or you can look at Christian book sellers such as the Evangelical Christian Publishers Association for more information on fast selling fiction.
Read the reviews. If you want to take a more critical look at Christian fiction start reading some of the better review sites. Begin with the Christian Fiction Review, which provides readers with Christian based critiques and evaluations of contemporary Christian literature. You can also read the book review sections of more general sites such as ChristianityToday.com.
Get a populist view from the blogs. If you're finding the Christian review sites a bit too highbrow or even boring, look at the Christian weblogs for reviews from readers who are probably very similar to yourself. Check out Dee Stewart's Christian Fiction blog, which speaks about the genre from the perspective of a writer. Turn to the Faith*in*Fiction blog for a few different viewpoints on the topic.
Use the power of Amazon. Amazon probably pops into your mind when you're thinking about books in general, and the same should hold true for Christian fiction. Search "Christian fiction" to find a list of books in the category. Amazon's powerful technology gives you critical reviews, reader reviews, a synopsis and numbers about how the book sells in various categories.