Kanji Converter is an interesting online tool that lets you paste Japanese text to convert. Well, there are other options for that, but where this one differs is that you can toggle different display options on and off. For example, you can show furigana or romaji and English translations. You can highlight all the words by part of speech (nouns, adjectives, particles, etc.). Clicking on any word will show the definition and link to similar words.
Editor’s Note: this site used to be free but now the free option is limited to 75 characters. Donate $10 per year to unlock this restriction.