At different times, there were different books.
The Night and the Dragon was probably my first favorite, then Strega Nona, and Alexander and the Terrible Horrible No Good Very Bad Day.
The Harry Potter books were next, and the Goosebumps series, and Aliens ate my Homework. Oh--and the Boxcar Children, whom I'd forgotten about until this thread.
And finally I moved onto things like The Westing Game and The Mixed-Up Files of Mrs. Basil E. Frankweiler.