Wikipedia
HR.com
HR.com is the largest social networking site dedicated to human resources professionals.
HR.com members have access to articles, case studies, newsletters, polls, discussion forums, blogs, webcasts and other features. Majority of the content on HR.com is community generated. The site is "similar to Facebook, with a business community" and allows HR professionals to share best practices and research techniques.
HR.com is an HRCI approved provider. and offers certification for HRCI ( SPHR/PHR) and for SHRM ( SHRM-CP and SHRM-SCP) programs.