There are about 3500 spider species in the U.S. and Canada, with hundreds of them occurring in each state. It is very difficult to make a reasonable guess about a spider ID without seeing the animal.
You probably have no reason to be concerned. Very few North American spiders are dangerous to humans and spider bites occur much less frequently than people think. Even in places where humans live with more than one dangerous species, bites are extremely rare.
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 books.
In addition, some useful Web sites include:eNature ZipGuide to the Poisonous and Dangerous wildlife in your area.
We hope this helps,eNature Naturalists