My proper introduction to reading murder mysteries was via my mother's stack of Agatha Christie novels. I'm not sure which character I loved the best - Miss Marple was certainly right up there - but I do know I identified most with Ariadne Oliver, the snoopy mystery writer who was often considered Agatha Christie's alter ego.
Dame Christie's grandson, Mathew Prichard, hosts a wonderful website. On it, he writes occasional blog entries, and the site itself has all the info you could ever want, including some freebies, like free games to download!
So visit the Official Agatha Christie website and take part in Christie Week!
From a writer's viewpoint, though, there is another wonderful website. Agatha Christie's Homepage offers a fabulous rundown of Christie's writing methods, her detectives, her plotting methods and the influences on her writing. Don't miss their links page, where you will find not only many other sites pertaining to Agatha Christie, but links to websites about Margery Allingham, Dorothy L. Sayers, and others! I urge you to take a look!