Ivy and Mader Philatelic Auction
One of the top auction houses in this field. They include auction features and many times there full catalogue on line.
Sotheby's
For over 250 years, Sotheby's has been going about the business of offering art, in all its splendid forms, at auction. No matter what your passion -- photography or folk art, Swiss watches or French wine, furniture or paintings, books or baseball cards -- you can indulge it at Sotheby's.