J-J Dictionaries

There are arguments for and against, but I think eventually anyone going for normal, educated adult level fluency in a language will begin using monolingual dictionaries at some point:

Why Monolingual Dictionaries should be used

How to begin using them

Samples:

http://dic.yahoo.co.jp/dsearch?enc=UTF-8&p=町&stype=0&dtype=0

http://www.sanseido.net/User/Dic/Index.aspx?TWords=野郎&st=0&DailyJJ=checkbox

http://dictionary.goo.ne.jp/leaf/jn/161897/m0u/飛行機/