Now I'm teaching Japanese for beginners in Arizona State University as a TA.
Many students ask me how to improve their Japanese by themselves online and I always tell them these sites beneath.
[Reading, listening]
NHK NEWS WEB EASY: http://www3.nhk.or.jp/news/easy/index.html
you can read and listen news from Japan in easy Japanese.
[Writing]
lang8: http://lang-8.com/
Lang8 is a site for language learners. you can ask japenese people any questions about language on this site.
[(advanced)Listening]
NHK RADIO NEWS ONLINE: http://www.nhk.or.jp/r-news/
Japanese WEB radio. I guess they read articles too fast to listen for foreigners.
I hope they will help you : )