All-American Collectibles - This site seems to be especially strong in baseball, but basketball, football and hockey are also represented; also team signed memorabilia and an on-line auction
Authentic Signed Sports - Almost everything on this site is signed and authenticated, although there are a couple of sections for unsigned memorabilia
Autographed Memories - A wide selection of authentic autographed sports memorabilia, plus a good brief introduction to collecting
B & J Collectibles - Nice on-line catalog allows you to look at items by price as well as by sport; be sure to look at the Web Specials
BobsArchives - Specializes in pro and college football and basketball programs beginning in 1893, also has some other memorabilia
Boxing Memorabilia - Most of the material here seems to be rather recent, but I did spot gloves signed by Jack Dempsey and Joe Louis
Cardboard Memories - It sounds like cards, but it's mostly autographed memorabilia, a lot of it recent, but also older things such as Mantle and Dimaggio baseballs, Joe Namath helmet
Dave & Adam's Card World - Dave and Adam really do cards; they have a big selection from most sports, weekly specials, weekly drawing for gift certificates and links to their E-Bay auctions
Elite Memorabilia has exclusive rights to autographed and game-used memorabilia from several athletes, including Michael Vick and Emeka Okafor.
Frameworth Sports Marketing - The emphasis is on hockey—they claim to be the world's largest distributor of NHL autographed memorabilia—but Frameworth also offers memorabilia from all other major sports.
Frozen Pond - Hockey only, and lots of it. The site says it has signed memorabilia from more than 300 past and present players, including more than 100 Hall of Famers.
Grandstand Sports Memorabilia - They have mostly recent memorabilia and autographed cards; they also arrange charity auctions
Hall Of Fame Memorabilia - Specializes in memorabilia autographed by Hall of Famers and today's stars; offers free shipping on standard UPS ground orders
ItsAlreadySigned4U.com Sports Memorabilia - Authenticated sports memorabilia obtained from major memorabilia vendors through private paid signings and a wide selection of sports display case products, some with NFL and MLB logos
MLBFanSite.com - A big selection of autographed MLB memorabilia, browsable by player, by team, or by item (i.e., balls, bats, etc.)
Nicko Sports Memorabilia - Very recent and current material from baseball, football, basketball, hockey, golf, auto racing, and other sports
The Pit - This unique site offers a Sports Card Exchange, complete with market report; it's affiliated, somehow, with Beckett
Player Autographs.com - A large selection of autographed equipment and photos, searchable by player or team
Pro Sports Memorabilia - The name says it; there's a wide selection from many sports, searchable by player or team; also, a brief but helpful intro to autograph collecting
Pugilistica Boxing Memorabilia - Here's genuine vintage boxing memorabilia, going back to bare-knuckle days; they have weekly auctions and they're looking for consignments
Signings Hot Line - Tracks athlete autograph signings in USA and Canada; also bulletin board, classifieds, and shopping mall
SI Galaxy - Many back issues of Sports Illustrated, Beckett Price Guides, Beckett Tributes, Sport Magazine & Inside Sports, as well as Newsweek & Time with sports covers.
Society of Olympic Collectors - Membership in this worldwide organization includes a subscription to a quarterly 48-page journal.
Sports Champs - At this site, you'll find a lot of Olympic memorabilia, including pins, badges. medals, posters, books, torches, and more
Sports Immortals - They claim to have more than a million itemsfrom just about every sport, and I believe it; the virtual gallery and video showcase make it an interesting place to visit even if you're not planning to buy
Steiner Sports Marketing - This is one of the biggest companies in the current signed memorabilia business, feature 10-20 private signings a month
Sweet Spot Online - No merchandise, but a lot of news about the business, including recent sales and prices, auction notices, and fakes exposed; there's a lot of free news on site, but they also offer a subscription for even more news
Upper Deck - Of course, they're famous for cards and other collectibles, but UD also offers autographed memorabilia and entertainment products
Vintage Sports Investments - VSI specializes in memorabilia from the 1950s, 1960s, and before; they're actively buying, and a current wantlist is posted on site; they'll also work with your wantlists, and they do insurance appraisals for collectors