There have been a couple of threads with ideas for good books. Check out the 'living books' section of the forum and browse through the last 3 or 4 pages.
One thing that has motivated my kids (DD7 and DS5) to read more of the living books that I want them to develop a taste for, is that I'll read the first few chapters of a book, just one chapter a day. After a few days, I find they are taking turns sneaking the book into their room to read it for themselves. This works especially well with my son, who often turns down books that I suggest until I've read a few chapters. I've done this with books like Trumpet of the Swan, Wizard of Oz, Follow My Leader, the Boxcar Children, and several of the Thornton Burgess stories, all of which he protested even listening to until the 3rd or 4th chapter, and then started reading on his own because he couldn't wait for the next chapter.
I do allow them to pick out books at the library, which sometimes includes things that might not qualify as high quality 'living books', as long as I have read a couple of books of the series and am comfortable with the content. The current favourite series are "Magic Treehouse", "The Puppy Place" and "Kitty Korner" (about families who foster dogs and cats and find them good homes.) These are just fun, quick reads that both kids love and reread over and over again until they are due at the library.
Other than the SCM literature suggestions, one resource I really like for ideas is: http://www.classical-homeschooling.org/celoop/1000.html