two useful Japanese learning tool sites
 

Denshi Jisho - Online Japanese dictionary this is the most awesome dictionary I could find

Tim's Takamatsu - Language Related Basic intro to Japanese verb , adjective , particle

With these two sites , you could get hold of Japanese quickly.

Awesome sites! If you're cramming for the JLPT test these two websites are very useful too:

Speedanki.com Kanji Memorization: online flashcard system to help memorise those difficult kanji

JGram - The Japanese Grammar database: all the grammar need for the different levels of the JLPT test

I will suggest a website also:
You can learn Kanji here.