Online Dictionaries

There are several good choices available.  For offline dictionaries, see Software
Simple, easy, based on WWWJDIC is www.jisho.org/

The ever popular yahoo dictionary -- note that you can switch between 大辞林　and 大辞泉 for the 国語辞典.

Goo is also quite popular : click me

ALC has a wealth of information, including their online dictionary

The man behind all the WWWJDIC has this site, including his dictionary page.