Apply! Apply! Apply!
It's true. Finding a job that you like is not easy, but if you approach your decision with a sense of purpose, you will be one step ahead of a competitor who puts it off. Don't let your newly drafted resume and cover letter sit on a shelf collecting dust. You've completed the difficult part. Now it's time to enjoy the fruits of your labor.
With a few rare exceptions, we don't think you can ever hurt yourself by applying for too many jobs. Perhaps if you're in a very small town, where everyone knows you (and your current boss), this is not a good idea. Or if you are applying for so many jobs that you haven't the slightest clue to whom you're writing or why, you should probably slow down.
But outside of these situations, you should be open to exploring as many jobs as possible before settling on one. See what kind of responses you get. If you're looking in more than one geographic area, is one area "biting" more than another? Are you having better luck with small vs. large companies? Applying for numerous jobs will give you a good feel for the job market and how you fit into the current demand.
In addition, each interview you go on will be a valuable learning experience. Interviews can teach you about the effectiveness of your resume and cover letter, what works and what doesn't as far as interviewing techniques, the types of questions asked most frequently, how to handle yourself under pressure, and the differences between various employment environments. Even if all you learned from your interview was that you would rather die than work for firm X or company Y, you still learned something.
Another parallel can be drawn to car purchasing. Those in the market for a car are advised never "to fall in love" with a particular car. This is so that you can walk away if the deal isn't right. The same goes for jobs. If you wait to send out that lovely resume until the absolutely perfect job comes along, you are only going to hurt yourself. Yes, maybe you'll land that job and live happily ever after. But it is more likely that 1) you will nervously sit by the phone every night, accuse your roommate/wife/kids of losing messages that never came, and attack your mailman until you drive yourself into a sleepless stupor, only to never even get an interview or 2) you will excitedly go on the interview sporting a new $1,000 suit only to find that the $120,000 job in an office overlooking the Pacific is a $20,000 job (the "1" was a typo) overlooking the Pacific Gas Company.
The more job descriptions you read, letters you write, people you speak to, and interviews you go on, the more you will learn about yourself, your needs, your qualifications, and your marketability. Many people have said that they learned a certain thing was misconstrued on their resume because of an interview. So maybe they didn't get that particular job, but chances are they fixed the problem and got the next one.
The key is organization. Keep a chart with the name of the employer, the type of position, and the date you applied. This way, when someone calls, you can quickly find out who it is and what position he/she is calling about.