You might also enjoy "The Complete Enchanter" by L. Sprague De Camp. I have not found an ebook version but it is a fun read if you can find the paperback at a used book store or even used online.
http://www.amazon.com/Complete-Compl.../dp/0671698095
it's a simple read and I was completely taken with it when I accidently had nothing else to read and it had a cool cover art at a garage sale a long time ago. My first exposure to the sci-fantasy with time travel genre and might be what you are looking for...
I can second the recommendation for the 1632 series over at Baen's free library. I am hooked on them. It takes the concept to the farest edge of what could be imagined. Very fun reads.