A social network for business professionals and career-minded folks, LinkedIn gets respect from the corporate world. Employers use it to recruit new talent; employees use it to network with others in their field. When you create a profile, treat it like a resume. You can build your personal contacts list by searching for, reaching out to and adding individuals who work for the same company, went to the same business school or know you from a previous job. Ask an old boss or partner to post a recommendation that others can view. The site's search filters help you find experts and contacts by company or industry. Basic accounts are free, but you can pay for premium service that grants you greater access to the network, which now boasts more than 11 million users. There are corporate memberships too, and all 500 of the Fortune 500 companies have signed on. Looking for a general-interest MatureSpace? check out Gather.