If you're looking for cars, checkout Carpoint where you can do everything short of actually feel how the car handles the road.

If you are traveling, you must look at Expedia for flight, rail, hotel and car rental reservations and purchases.  I can not say about the ease of use and the quantity of detailed information available through this service.

Of course the absolute best way to get books is to use Barnes & Noble.  I can not tell you enough how much better this is than any alternative I have yet encountered.   Not only are the prices lower, and delivery faster, but you save the trip to the store, you can shop in the middle of the night, and my friend Albert Kim architected and managed the creation of the site!!  Woooohoooo!  Of course it has changed a lot since then, but it's amazing to me that I actually know someone who built the first version of one of the web's most successful e-commerce sites!  You go, Bertie Baby! I used to recommend CD Now for CD's, but now I find that Barnes and Noble has a great selection, as well.  Be sure to check them out here.

If you're looking for general merchandise and do not feel like going to a department store, look at iQVC for some good deals.   Beware the closeouts and discontinued models, though.

I have fallen into the Gap, and I have been very happy with the experience.  I cannot believe how quickly they turn around orders there.  I had an excellent shopping experience there.