The Persona 4 Spinoff Catalouge
Doubles as both a catalouge as well as series of reviews on various Persona 4 supplementary materials. Also contains links to some fantranslations of otherwise unreleased content.
Emperor
A fanpage dedicated to Kanji Tatsumi from Persona 4. A work in progress at the moment, contains minor spoilers for Persona 4 as well as other spinoff titles.