For general infomation, try Gilbert and Sullivan Archive Home Page which has information on all the operas and much besides.
If you are interested in recordings of the G&S operas you should definitely visit, The Gilbert & Sullivan Discography Page. This site is a true gold-mine of information on G&S recordings from the first attempts at near-complete recordings in the days of the recording horn right up to the present day.
One of the finest singers in the history of the D'Oyly Carte Company was Darrell Fancourt. It is well known that he was a pupil of Lilli Lehman but the circumstances may not be so well-known. In this newspaper interview from 1938 he described how he started out as a singer.
On occasion I have been known to write short pieces of fake history to fit the stories of the operas into a context.