This site has a lot of information and provides good lessons for beginners as well as advanced learners. You can also test your German proficiency there.

From Website

Learn German online and for free: 10 German lessons for total beginners and 24 German grammar lessons for advanced learners are complemented by numerous interactive German exercises, an introduction to new German orthography and 2 online German tests to improve and to evaluate your German proficiency.

Study tips, famous quotations, an online dictionary to translate German terms into over 70 languages and international penpals complete our free services for learning German!