The hottest item is a 2004 Donruss trading card that portrays Phelps as a celebrity fan of the Ravens. The Texas company released 300 autographed versions of the card and about 5,000 "common" versions with no signature.
"This Phelps thing has been phenomenal," said Tracy Hackler, associate publisher for Beckett Media LP, the most quoted price-setting company for sports cards. "The card had essentially been forgotten about."
When the card was released, the autographed version sold for no more than $30 and the common version for less than $1, Hackler said. Even two weeks ago, the autographed version was available for $40.
"It was a nonfactor," Hackler said.
Now, he lists an autographed Phelps in mint condition at $800 and the unsigned version at $100. That's probably the peak, Hackler said, because the frenzy over Phelps' accomplishments will wear off in a few weeks.
"That'll probably be a $100 card in two months," said John Conigliaro, who owns Great Moments card shops in Westminster, Timonium and White Marsh.
An even rarer Phelps card from Upper Deck (10 were produced) sold for $2,550 Monday night on eBay.
Sudden surges in value are common in the trading card industry, but Phelps' situation is unusual because of the magnitude of his accomplishments and the rarity of cards bearing his likeness.
"The thing that impacts a card's value more than anything else is a man's performance on the field," Hackler said. "People want to remember where they were when they saw him do these things. It was a transcendent moment for them."
An eBay search yesterday afternoon turned up 2,021 Phelps items. There were "Phelps Phans" T-shirts, old photographs and magazine covers. You could buy into Internet domain names featuring the word Phelps. You could even buy a Phelps snow globe.
Authenticated USA swim caps autographed by Phelps went for $1,000 or more.
Conigliaro said he's taking about 10 calls a day for Phelps items. Later this week, he'll start selling for $199 framed swim caps that Phelps signed in 2004.
He doesn't expect them to stay on shelves for long.