BLers - but especially translators - don't know what something in Japanese means? Need help with your homework? Post your questions here.
Well, back then it was mostly me, but hey.
Useful tools I've found:
Yahoo! 知恵袋 - Yahoo! Answers Japan. Generally good for "what does ___ mean?" A lot of helpful people here. They are not always correct.
Rikaichan - instant and intuitive lookup in Mozilla Firefox. Now with names!
*Rikaikun is now available for Google Chrome! It doesn't have the dictionary updates and additional databases of Rikaichan, however.
Tae Kim's Grammar Guide - rather basic, but a solid reference with good explanations
Kotobank - Dictionary good for idiomatic/figurative language or otherwise phrases that aren't found in standard dictionaries. *has become somewhat more difficult to navigate since integrating with Yahoo!.
JGram JLPT level 1 page - Most elementary grammar can be found all over the web, but this does a good job of explaining some of the more difficult Japanese grammar, in English. Much of the content here can only be found elsewhere in Japanese-language textbooks.
姫語録@Wiki - Japanese onomatopoeia.
Try to rely on Japanese-English dictionaries as little as possible.
At work, I also found some useful documents which should help anybody in editing work.
Military Ranks and Groups - contains easy-to-understand explanations and approximations of divisions in military rank and organization. Not so useful for Type-Moon, admittedly.
Archaic English How-To - A handy primer to getting your King James on. You'd be surprised how bad many writers are at this.
English Grammar 1 - well-written, comprehensive reference
English Grammar 2 - handy, quick reference