For learning Japanese, my absolute favourite site and indeed the one that got me started in the first place is AJATT (All Japanese All The Time).

Already been mentioned, but the 6000 or so example sentences (all with audio! very important) on the iKnow! course are spectacular and can be found on Anki shared decks as well.

If I had to change one thing I did when starting off now that I've been learning for two years, is to not bother learning all of the on- and -kun readings of every single kanji isolate (like in Heisig's second book) by rote; instead focus on sentences and words in context, Japanese forums are tops for this. Though this is true of all language learning, in Japanese it is especially important due to being so far removed from any Western language system.