I have an old book that can't be beat, but, naturally, it is out of print. It was written by Gebert/Edwards. Ken Gebert passed away some time ago.
Edwards has a new book out that MAY be every bit as good and can be had here: http://www.go2atp.com/stores/1/product1.cfm?Product_ID=125
ATP (American Technical Publishers) has a few books that look promising, just type in "transformers" in the search engine block.
For just basic knowledge, the "American Electricians Handbook" is also pretty danged hard to beat.