This new semester marks my third year studying Japanese, and I don’t think I could have done it without jisho.org and its Kanji by Radicals index (jisho is dictionary in Japanese). In my Advanced Japanese class, we primarily review grammar and learn new Kanji, but the hardest part for me is that the instructions in our homework are in Japanese for the first time. Jisho.org has saved my life, or at least my homework, on more than one occasion this year, and for this I thank it.
Update (9/19/09): I recently discovered that Jisho.org also has a mobile version for iPhone/iPod Touch that works better than most dedicated Japanese translation apps. I highly recommend it!