Most "spell books" aren't too useful if you aren't experienced with advanced magick, however you can find tons of free eBooks by just looking up "free (whatever you want) eBooks" on your search engine c:
If you are beginning in Magick, then I'd recommend looking more into the basics and gain an understand of what Magick is before jumping straight into spells.
These are some good books recommended by Lark in the Forums:
"Before You Cast a Spell" by Carl McColman
"Spells and How They Work" by Janet and Stewart Farrar
"The Veil's Edge" by Willow Polson
"Modern Magick" by Donald Michael Kraig
If you are interested in buying books from the site, you can simply search through the shop: