Unless you're a newbie programmer you've probably figured out by now that it's always a good thing to stay on top of the job market.  If you haven't figured that out yet, here's why...

1. Things change. Have you noticed that annoying trend in TV shows where your favorite character gets a new asshole boss?  Well guess what, that happens in real life.  So do layoffs and acquisitions.  Point being, no matter how happy you are in your current job, things change.  Be prepared when they do.
2. Mo money. The unfortunate reality is that it often takes leaving your job (or threatening to leave) for programmers to get more than a cost-of-living raise.  Knowing what opportunities are out there will put you in a position of power when you sit your boss down to tell him he's not paying you enough.
3. Practice.  Interviewing is kind of a crappy process and the more you do it, the better you get at it. 
4. Know the market.  It's not a matter of if you look for something else, it's a matter of when.  Unless of course you expect to retire working at the desk you're sitting in now.  Scary thought, right?  Well when you do start looking around, wouldn't it be nice if you already had a good read on the companies hiring in your area?  Who's the new hot start-up?  What Fortune 500 company is looking for coders?

So now you know why you should stay on top of the job market, but how exactly should you go about it?  Some companies aren't very appreciative when they hear their employees have their names out there.  Sure, some would say those companies need to get over it, but you probably shouldn't rock the boat as long as they're signing your paychecks.

1. Don't sign up for Monster or Career Builder.  If you're looking to sell life insurance, then feel free to ignore this advice, because that's about 60% of what you're going to get if you post your resume on Monster.  The rest of what you get are going to be spam from recruiters.  Plus, if you're posting your resume on these sites, you might as well walk around the office in a T-Shirt that says 'Screw this place, I'm looking for a new job'
2. Work with a recruiter that you trust.  A lot of recruiters suck.  Those are the ones that send you endless emails with positions that aren't even relevant to your skill-set.  Some recruiters are awesome, truly have your best interest in mind, and won't bother you with crap job listings 3 times a week.
3. Sign up for n3rds.com.  Of course we're a little biased, but we built n3rds with the employed programmer in mind.   It takes less than a minute to sign up and after your profile is set up, you can completely forget we exist (though we'd rather you not do that).  Once you're signed up, our job discovery algorithm will identify your perfect opportunities and we'll shoot you an email with the information.  It's as simple as that.  And since we take privacy seriously, your information is never available publicly.  Recruiters and employers aren't allowed to search our users and the only way they'll know you exist on n3rds is if you apply for a job.