Heritage Auctions, one of the biggest internet auction houses, is currently auctioning off what is arguably the Holy Grail of Islanders memorabilia; the jersey Bob Nystrom was wearing at 7:11 of overtime on May 24, 1980. At that point, Nystrom scored the winning goal in Game Six of the 1980 Stanley Cup Finals to bring the Islanders their first Stanley Cup.
The jersey appears to have all sorts of rips and tears, likely due to the lengthy and tough playoff run and also has an Olympic patch commemorating the 1980 Lake Placid Games. According to the auction page, the jersey still has the fight strap on it as well.
As far as the authenticity of the jersey is concerned, blogging friend/enemy Scotty Hockey says that Joe Tomon, who the auction states provides a Letter of Authenticity for the jersey, is one of the most well-respected sellers in the game-worn jersey sector.