A business broker is an option, but as others have said, they follow a formula and may not understand the business and model. I've built and sold two ".com" companies, one of them a service company.
You're selling a services based business, so you are selling current clients that may buy additional services now or later, plus you are selling reputation and brand equity.
As one person said before it's about establishing value - the Valuation.
The "value" comes from the "goodwill" that is, customers you have, prospects in the pipeline and potential within your market.
In an economy like this, selling a service business is hard, but not impossible in finding the right buyer.
The buyer may request you stay on for a "transition period" if you have very good relationships with clients. This can be anywhere from 6 months to two years and should come with a salary. There will likely be layoffs and they are related to trimming jobs that are the same. It's also a chance to get rid of "poor performers" for both buyer and seller who will site "efficiencies" as the underlying reason.
Culture: This is a big factor in a buy-out. When it happens it will take 12-24 months to "assimilate" the culture of the buyer and bought and is perhaps the hardest part and least recognized, part of an acquisition.
In setting a valuation, be sure to count your Web presence; inbound links, page rank, search ranking etc, as this has intrinsic value. If you have a
PR of 5+ that is good and means a lot in terms of being "found" in your space.
PM me if you have further questions.