If I would have to pick only one, I'd have to vote for Roy Jones Jr. Granted, he's doing everything in his power to **** up his legacy over the last few years, going 7 wins with 7 losses since 2003 is really ****ing up his numbers.
Anyone active? Hearns, Holyfield, Tyson, Jones, Hopkins, Floyd, De La Hoya, Mosley, etc. (only a maybe on the last 3 though).
Active in the Last 10 years? The Fab 4 Featherweights are all legends; Hopkins, Jones, De La Hoya, and Mosley can be said to be as well, and I think will be referred to as such in the future; Floyd will be famous but may lack the in-ring drama in his career to be called a legend. The Klitschkos are special in their place in history considering their relationship as brothers and utter dominance in the sport. EDIT: Forgive the inclusion of non-US fighters, misread the thread.
Hearns, Holyfield, Jones Jr, Hopkins. Floyd could be considered a legend by the time he retires depending on the outcomes of potential fights in the future.
Hearns, Holyfield, and Tyson. and you'll notice they are all relics from the 1980s Roy Jones Jr and Bernard Hopkins will go down as great fighters. Floyd Maywether too. Perhaps DelaHoya and some others. But I wouldn't call them "legends". Jones might be the closest to it, on sheer mythical skill in his prime, but his lack of epic fights probably prevents it.