This section will doubtless be eternally under construction. Right now, you can try...

The Rose Of Versailles. Incredibly detailed and helpful. <3!
Glory - a Berusaiyu no Bara compendium. A lovely introduction to the series, with character profiles, scans and screencaps. And an excessively amusing movie parody. XD
BeruBara. A livejournal community dedicated to the series.
Versailles Dreams. Fanfiction, fanart and all that shiny stuff.
Which Rose of Versailles character are you? A silly quiz I made, because I felt the fandom needed one.

And some more real-world-based historical information...

Axel de Fersen. A brief introduction to Axel and his life. In French.
Steninge Slott. Axel's childhood home, with some brief information on him and on the house itself.
Letters between Axel and Marie Antoinette, and between Axel and his sister.
Marie-Antoinette.org - information on Antoinette, with a rather impressive image gallery.