Oh I am so excited to find this thread! What a great idea! We are all book fiends at our house, and finding quality books of an appropriate reading and interest level can be so challenging. I especially appreciate people including notes on scary topics for sensitive kids.

I second the Magic Tree House Series suggestion. Those are the books that really got my DD5 excited about reading on her own. She just couldn't wait for me to be available to read to her. We have found that a few of them have topics too scary for her such as ghosts and mummies, but they are easy to avoid.

For science enthusiasts, I recommend the Magic School Bus chapter books. (Not the MSB picture books, though those are good too for a lower reading level.) They are at a slightly higher reading level (~grade 3.5) than the Magic Tree House books and are packed full of science facts. They are about a class of students who often take magical field trips in their school bus with their eccentric teacher. Each book concentrates on one topic such as space, bones, or bats. My DD5 is very sensitive to scary topics and has not been bothered by any of these books.