CASEBOOK JACK THE RIPPER
By far the most in depth and useful online resource, Casebook.org is maintained by Stephen Ryder and offers you everything you could possibly want to know about the case and the history of the east End.
In addition to maps, a photo archive and a huge number of contemporary newspapers, there is also a very lively forum on which you can discuss the case and post questions.
THE JEWISH EAST END CELEBRATION SOCIETY
The Jewish East End Celebration Society aims to focus attention on Jewish life and culture in the East End of London. In addition the society provides a great deal of information on life in and the history of the Jewish East End. Their website, consisting of well written articles, fascinating insights and also comprising a photo archive, provides an invaluable resource on all aspects of the Jewish East End and its history.
THE METROPOLITAN POLICE
The Jack the Ripper murders were investigated by various division of the Metropolitan Police whose headquarters were, and are, located at New Scotland Yard. On their website they have an excellent overview of the Jack the Ripper case. You can also study the full history of the Metropolitan Police.