Study Japanese Vocabulary:
http://kanji.asianmideast.duke.edu/
http://www.jlptstudy.net/
www.skritter.com
http://www.digitaldialects.com/Japanese.htm
Japanese Dictionary:
www.jisho.org
www.japanese.nciku.com
Writing Skills:
http://japaneseup.com/ (click the "x" to get rid of initial window)
Japanese Grammar:
http://www.jgram.org/
Listening Practice:
www.japanesepod101.com
Reading Material:
http://www3.nhk.or.jp/news/easy/ (beginner level)
https://matcha-jp.com/easy/ (various levels)
Japan Travel Magazine
http://www.ajalt.org/kanmana/index_e.html (intermediate/advanced level)
Culture, Vocabulary, Lessons, Sentence Structures:
http://www.japanese-online.com/