And while we're on the subject of French, I should also mention another powerful online tool. It's an online grammar and spellchecker for speakers of French (native or not). The tool, www.lepatron.ca, is a writing assistant rather than a corrector. Rather than correcting grammar and spelling errors automatically, it flags mistakes thereby allowing the user to introduce their own changes.
As I'm not a "francophile fanatique" like he is, I don't need that site, but it's still very cool in case you want to write correct emails and other French text.