BBC: Learning English This site contains videos, podcasts, lessons and quizzes to help you improve your English skills. Note: this would be "British" English, not U.S.
Engvid Videos including Business English, idioms, pronunciation, slang and more.
Livemocha This site has free and paid online courses. You will need to register to use the system (there is no charge to register).
Englishyappr.com Register (it's free) then take a placement quiz and start practicing and learning.
New York Public Library Learn English Using Online Resources This site links to several English learning websites.