Linkedin.com – From a headhunter’s standpoint, LinkedIn has it all. It is the opportunity of a lifetime to establish a powerful network of influential colleagues and friends – can you tell it’s my favorite? Free to use, Linkedin.com first requires you to set up a profile, then invite your friends to join your network. After those people join, they can ask their friends and colleagues to join, etc., etc. For job hunters this can produce a treasure trove of leads. More than 9 million people have linked up at LinkedIn.

Classmates – This may be the grand daddy of online networking sites. At Classmates.com, you can join a network of alumni who share an affinity with you – they went to the same school (high school, college or university), or were in the same military branch, industry or company. The challenge, when finding potential contacts, is that you must search by state. But, if you want to reconnect specifically with people you went to school with, Classmates is the way to go.

ExecuNet – If you make $100,000 or more in salary, this networking venue is for you. ExecuNet was founded 18 years ago as the premier networking web site. They make it easy for senior-level professionals to connect directly with business decision-makers, executive recruiters, and peers. Not is this site chock full of helpful advice that’s not found anywhere else, they also host well-known speakers and authors. Of course, I’m biased because founder Dave Opton wrote the foreword for my book, Guerrilla Marketing for Job Hunters.

Here are four more networking sites with benefits too numerous to list. I suggest you join at least two sites, then use them as aggressively (staying within the rules, of course!) and creatively as possible.

Ryze – A classic. Robust and easy to use. Not only can you use it to connect with people online, it may put you in touch with someone in your city – there’s an in-person networking component to the site. It’s the best of both worlds really.

Spoke -- Great for connecting with sales people of all types and Fortune 1000 companies in particular. Sales people, by the way, are great resources for job hunters – they’re naturally outgoing and often willing to help. This site boasts more than 30 million contacts and 900,000 companies.

MySpace – Check the Groups Home page, where you’ll find people clustered by interest. The site also has a career space. Truly an 800-pound gorilla in terms of size and scope … and still growing.

Heartless Bitches International – This site is for women who like their career advice with a dash of spice. (Er, make that a handful.) Plus, you can hobnob with some of the most intellectually stimulating women on the planet. That’s Heartless Bitches International.

Double bonus! Here are two more sites to help grow your network …

The Social Networking Web Log is loaded with tips to help you reach inside target companies.

College Recruiter isn’t a social network. OK, so sue me. But it should be on your networking read, especially if you’re a college grad. There’s an encyclopedia’s worth of advice there.

Article by David E. Perry Managing Partner of Perry-Martel International Inc., co-author Guerrilla Marketing for Job Hunters and Kevin Donlin, President Guaranteed Resumes, author, Resume and Cover Letter Secrets Revealed, Guaranteed Sales Resumes, and 51 Ways to Find a Job Fast -- Guaranteed. David and Kevin are co-authors of Guerrilla Resumes