The current economic climate makes it a tough market for job-seekers. Things are getting better now, but I think that since about 2000, the internet has changed the job search market faster than the theorists can write books.
I believe that networking -- the personal kind -- has always been important, and is now critical. Every job opening gets hundreds of letters from around the country because more people can search the Internet than (say) the Boston Globe--and they can search it more easily. Emailing résumés is easier (and cheaper) than printing and mailing them (You've probably heard stories about people emailing hundreds of resumes.) So the personnel department has to separate the wheat from a lot more chaff.
Just because you've spent hours customizing your resume and cover letter doesn't mean that the personnel department will even give it more than a glance. And the best qualified candidates often don't make it past the personnel department. Some companies and recruiters are doing a lot with automating resume searches, but at this time, I think networking is the key to getting your resume directly to the hiring manager.
I think that you have to find a job opening, then find someone who you know that knows someone at that company (or knows someone who knows someone at that company.) I believe that the internet provides two types of tools for doing this. One is job search engines like monster.com. The other is personal networking engines that use "degrees of connectivity" to help you find someone who knows someone who knows the hiring manager.
Part of your network involves all of the sales people who you've been in contact with. They generally won't know of any job openings, but if you can identify a company they may be able to connect you with someone inside that company. After all, their job is to contact people like you at a large number of companies. Sales people will generally try to help you out if you have at least an OK relationship with them. If you've done them a favor or have a great relationship with them, they'll do more for you. Sales people aren't headhunters--they won't find a job opening for you, but they may know someone at the company you've identified.
Indeed.com -- interesting job search engine, seems to be based on Google.
LinkedIn has a jobs search engine
The Ladders claims to have six-figure jobs.
Telecom Careers -- Telecom oriented career site
Dice -- Technical career site