I am going to review a website I first used for studying Japanese before going to university:
Japanese Grammar Guide | Tae Kim's Guide to Learning Japanese
This site is really good as a supplement for people in their first year studying Japanese and even goes as far as covering some JLPT N2 (maybe N1 as well) grammar points. It's in an easy-to-understand tutorial format and also forces you to know at least kana (kanji have labels when you hover over them so you can read them, or at least until the later chapters).
There is also JLPT Study page which is a great site for those trying to study the JLPT vocab and kanji, but unfortunately this site doesn't provide everything. The grammar list is limited. I believe they're in the middle of updating it.
@pandaman101: Yes, Japanesepod101 is a good listening supplement. I would recommend it, especially to those at an intermediate level of Japanese. It can get a bit repetitive for advanced level.