(I'm cutting and pasting from another question I answered elsewhere.)
Here's the link to the WritingWorld advice on agents: http://www.writing-world.com/publish/index.shtml#agents
I've actually been doing some research on publishing and agents while I've been working on my book, as well. Here's some of the information I have found. One thing is certain - a reputable agent never gets paid up front. Their pay comes when they've done the work for you and found the publisher. So if any agent is asking for fees up front - it's more than likely that they're shady.
I found this excerpt from "Finding an Agent" by Judith Bowen on absolutewrite.com.
-Check out books in the library that list literary agents. [Like “A Guide to Literary Agents” published by Writer's Market] See if they are members of reputable professional organizations. Go to writers' conferences. Talk to other published authors. Gradually put together your own short list and send out query letters describing your manuscript--the fact that yours is completed is a plus-- starting with the first agent on your list and working your way down. Chances
are, none of them will take you on.
Don't give up. Get out there and sell your manuscript to a publisher. Contrary to what you might have imagined - that it's the agent's job to sell your book - the truth is, your book is going to have to sell itself, whether you send it out or an agent does. Then, when you're offered that contract, contact your short list of agents again, starting at the top, and mention you've got a contract to negotiate and you'll be pretty pleased to find that the response will be quite different. Maybe your first choice or your second still won't be interested, but your third or fourth will. If you've done your research, he or she will still be a fine agent with a good reputation. -
Here are "Seven Essential Points on Literary Agents":
Another good idea for looking for an agent is to read books similar to the ones you want to publish. See if there's any way you can find out who their agent was. It's best to know who else the agent has represented, especially when querying. It lets them know you've done your research.
Once you've done that research, check out if the agent is listed here at Preditors and Editors: http://www.anotherealm.com/prededitors/peala.htm
It’s a link to a list of literary agents, but it's alphabetical, not by genre - but this is from a reputable group that looks out for a writer's best interest. Don’t query the ones with the red “Not recommended” notes.