Jim,
The V. & A. is your best bet as far as a regular museum of decorative arts goes. I spent a lot of time there when I was a student in London. A look through what might be available for viewing at some of the National Trust's historic holdings can provide some fun side trips. Also, check the schedule of sales for auction houses such as Christie's, Sotheby's, etc. If they are previewing a furniture sale, it will be an opportunity to actually touch some very fine things. PSP