Akemi's Anime World: Filmography.
Hitoshi Doi's Seiyuu Database: Provides information on voice roles, CDs, books, radio and events.
Mitsuishi Kotono International Fan Club: Their newsletter can be downloaded here.
Perry and Ansatsusha's Seiyuu Page: Anime list with character images.
Various Emotions: A fanlisting uniting all fans of Mitsuishi Kotono.