This site specializes in soil survey data. It has a link to the Global Change Program of the NRCS, which is particularly interesting. The National Soil Erosion Research Lab at Purdue. This link goes to the home page for the FAO, whose mission includes soils, but also agriculture and food resources around the world. This site has more links to agricultural and food resources than to soils, per se.
Many universities have programs in soils.
Please let me know about any other interesting sites you find. I'm particularly interested in locating some more sites with good pictures of soil profiles.