There are about 3500 described spider species in the U.S. and Canada, with hundreds occurring in each state and many more awaiting discovery. To learn more about your local species, here are some recommended books:
Spiders and Their Kin (Golden Guide) -- Herbert Walter Levi, et al. This tiny book is full of great figures that show basic family level characters (such as eye arrangement) and has pictures of many common U.S. species.
How to Know the Spiders -- Benjamin Julian Kaston. This is a more technical book with many detailed anatomical figures.
Anybody who takes the time to wonder about the identity of these fascinating creatures will appreciate these resources.