Huston Smith's "The Worlds Religions" is very good. It covers the major traditions. He is very readable and an expert.
I recently picked up "The Complete Idiot's Guide to Exploring God." It goes more into the various religion's
ideas of God, rather than into the religions themselves. It covers different views of God, like monotheism, pantheism, panentheism, monism, etc ... It gives a good insight into the beliefs, rather than the history.
I also picked up "The Complete Idiot's Guide to World Religions." It is a very shallow and brief exploration of the major religions from a comparative viewpoint.
Hands down, the best books on comparative religion are by Keith Ward. However his major comparative work is a four volume set, so it's not brief.
And although I haven't seen it, The Teaching Company has a course on "Great World Religions." It's on sale right now and is available in DVD, VHS, CD or audiotape format. Here is the link:
The Teaching Company - Great World Religions