Diablo 2 SuperStore
Items and accounts for sale across all realms.
Mephisto's Closet
Various Diablo II items of sale, sorted by realm, with forum and affiliate program.
Offd2.com
Sells virtual items for use in the game, at USEast, USWest, and Europe.
RPG Traders
Searchable auctions and trades for each realm, version, and mode.