The most common question that other writers ask me is "Do you have an agent?" And most are surprised when I say no. I've sold seven books to publishers throughout the U.S., including one novel to Wizards of the Coast, without an agent.
I love the idea of having an agent: somebody to sell my work, read contracts, and make sure royalties are paid on time. In the best of all possible worlds, somebody who cares about my writing, gives me suggestions on how to make it better, and maybe even mentors me through the ups and downs of pursuing a writing career.
And there are agents out there who do all those things. I know that. And I think paying them 15% of earnings is more than fair if they are the ones establishing where I can earn those earnings.
However, I've always found a market for my work without an agent. Mostly because I like to sell before I write (it's a time management issue), I've pursued publishers who accepted queries and issued contracts before I completed the manuscript. I could have gone back and gotten an agent to handle the back end of the process, but I don't find reading contracts intimidating or troublesome. Most publishing contracts are straight forward, I can cross out anything that I don't like, and (sadly) I never thought I had a project worth so much money that it would pay to involve an agent or a lawyer to close up possible loopholes.
Realistically, I write for the midlist, not the bestseller list. Niche nonfiction, genre fiction. And for that market, you can find publishers who are willing to work directly with the author.
Now, should I get the big bestseller idea, the Oprah book, the one that I know will sell millions, I would go look for an agent. But until then, I'll keep chugging along, working with publishers who want to work directly with me.