The first book I consistently re-read was "The Swiss Family Robinson" by Johann Wyss. I started reading it in high school and then just kept reading it. Another book re-read quite a bit was "Little Fuzzy" by H. Beam Piper, I'd probably have read it more often but it was the book I would give away to friends to get them interested in Science Fiction. One series of books that I have read often over the years was Griffin's "Corps" books (had to re-read them when a new one came out, did the same with Weber's Honor Harrington). Last few years I've been stuck on Elizabeth Moon's "The Deed of Paksenarrion". You can get the first part of it in Baen's free library.
Sheep Farmers Daughter