For those who prefer their own tour there's this new great official app with 15 tours (5 are handicapped accessible) in Hebrew, English and soon Russian, to all parts of the Old City of Jerusalem.
You can get it here:
It's all guided by voice and GPS with offline maps, pictures and texts.
It's a service provided by the Jerusalem Development Authority (a governmental organization. Doesn't get more official than this :) for free with no ads, just lots of great information!