I've actually been working through a month of a paid subscription to Ancestry.com in fixing up a lot of missing citations in my tree. But I always love free research. So, when I stumbled upon this, I thought I'd pass it along.
If you have French Canadian roots, this source is invaluable and, I've recently discovered, free. It is the seven-volume tome, Dictionnaire Genealogique des Familles Canadiennes by Catholic Priest, Cyprien Tanguay. its a massive seven-volume set that spans 1608 to 1760.
PDF versions that are also free online, are SEARCHABLE!! - can be found here at the Many Roads web site. DJVU readers are easily found for free from places like SourceForge.
There is a companion to this over 2000-page wonder called the Complément au dictionnaire généalogique Tanguay by Joseph-Arthur Leboeuf, which contains 600 pages of corrections and annotations. As far as I know, this work is not yet available in the public domain.
Merci, Pere Tanguay!