The headless Scott Eric Kaufman over at Acephalous is putting together a list he calls "The Best Introduction To..." and he is soliciting help on the project, which needs more input from medievalists.
I've been trying to think of good suggestions for the "Anglo-Saxon" heading, and I've come up with several:
Greenfield and Calder's A New Critical History of Old English Literature
Katherine O'Brien O'Keefe's Reading Old English Texts
Godden and Lapidge's Cambridge Companion to Old English Literature
Of course, inherent in making any such list is the nagging feeling that you are leaving off some really important stuff, like Blackwell's encyclopedia, etc.
UPDATE, April 5th -- There is a good discussion of this topic over at New Kid on the Hallway, with some really good comments, and mentions of a lot of other good texts I didn't think of off the top of my head.