Japanese Dictionaries and add-ons
If you use an Apple/Mac, there is a built in dictionary that can also serve as a Japanese-English dictionary. Also on Macs there is a language input source shortcut. This means you can easily alternate between various language (English, Japanese, Chinese, French, Russian, etc.) settings when typing by holding down the command key and the space bar. First, you have to open the System Preferences. Second, select Language & Text. Third, select the languages you want to use.
Rikaichan is a great resource if you use Firefox, Thunderbird and Seamonkey.
If you have an iPhone or an iPod Kotoba or Japanese are great dictionary apps. Kotoba is free and Japanese is less than 2000円. You can find both through the Mac App Store.
Pop Jisyo is a handy online dictionary.
Space ALC is another handy online dictionary with some amusing translations at times.
If you want to test your Japanese language skills try the Japanese Language Proficiency Test 日本語能力試験. It is offered twice a year in Japan and there are five different levels.
Learn Japanese Online JOI is an online Japanese school. Take small-group classes or private lessons, and learn real Japanese from professional Japanese teachers. http://joi-japonin.blogspot.jp/
Meguro Language Center offers a lot of free PDF worksheets for all levels. They are very useful if you are preparing for the JLPT.