Hi, Bill. The first thing to know about literary agents is this: Never, never, never pay one out of pocket. Not for a reading fee, not for an evaluation, not for anything. Not even if it's a small fee. Reputable agents get paid on commission when they sell your book to an advance-paying publisher.
Agents who have to advertise are not agents you want.
Good agents are agents who have sold books you've heard of to publishers you've heard of. Go through your bookshelves, and go to the bookstore, and find out who agented the books there that are like your book. Research them. Find out how to submit to them. There's no way of getting out of legwork.
Helpful resources:
Everything You Wanted to Know about Agents
On the Getting of Agents
Writer Beware
Preditors and Editors
Also check out the Bewares and Background Check board here on AW, particularly the
Index to Agents, Publishers, and Others
Good luck!