Persona II: Tsumi and Batsu - This person has a really good, comprehensive site.  And apparently the ability to understand Japanse and play Innocent Sin.  Which means I'm not sure if I want to gift her with boxes of delicious candy, or smash her kneecaps in a jealous rage. This is probably the place to go for the basic info you can't find here. 

Persona: Blind Faith - An original-character writer's RPG (read: PBeM) where one writes chapters for original characters.  If that's your sort of thing, mosey on over. 

PersonaFAN - a nicely designed site, and host to the Summoners' Network BBS.  Just about the only place I can think of to contact other fun shiny persona fans, it is.  Hooray for fitting names?  If only they actually updated...

Persona - Chaevel's site, which covers all three games.  Wander over for all your IS and Revelations needs. 

Atlus - they made Persona II, and translated it as well.  What haven't they done?  *sideways look at drooling IS-wanting horde.  which is promptly joined by yours truly - holding a board-with-a-rusty-nail-in-it, no less*

Parabellum - Wow. Just.. wow.  If I could draw even remotely like Karniz Archada, this site would be like hers.  But I can't.  So this won't.  Some amazing fanart here... and in fully understandable english! 

Rengedai Ward - this place aims to be a comprehensive series site, it seems, and already has an extensive overview of all the characers. I look foreward to seeing more from it.  You should look foreward to seeing it for the first time.  

The Ellen Shrine - A shine.  To Ellen.  See how madly informative I am? Let the fanboy congregation commence!

Innocent Soul Punishing Fate - snazzy fanart, and snazzier design that somehow manages to be both more practical and prettier than this one.  Roar.