Japanese Dictionaries
Skritter is great for learning kanji and words, but you're still going to need to look things up. Here are some of the best online Japanese dictionaries.
Denshi Jisho is a great online Japanese dictionary. It uses the EDICT dictionary file, and provides a great interface for searching by Japanese, English, kana, or romaji. They also have a kanji dictionary with a very slick component-based search, and a large corpus of example sentences.
The Yahoo Japanese dictionary gives you online access to some of the best printed Japanese dictionaries. More advanced learners will also benefit from the Japanese-Japanese dictionaries and multi-dictionary search options available there.
Correct Kanji Stroke Order is, as its name implies, a site cataloging the standard stroke orders for Japanese kanji. If you ever see a character whose strokes seem to be all over the place, you can come find the correct way to write it here.