Apart from some of those that have already been mentioned, in his last 32 fights following the lone loss of his career to Harry Greb, Gene Tunney notched a 31-0-1 (15) ledger, including 2 victories over perennial contender Charley Weinert, a newspaper verdict over tough Tommy Loughran, 3 victories and a draw over All-Time-Great and Hall-of-Famer Harry Greb, another Hall-of-Famer in Tommy Gibbons, a knockout victory over Hall-of-Famer, master technician and French war-hero Georges Carpentier, and two decisions over All-Time-Great Hall-of-Fame heavyweight Jack Dempsey. Not as numerically impressive as Sugar Ray Robinson's 88-0-2 run after his loss to LaMotta, but I think the quality of his opposition was better.
Bull****. Holmes is a toss up, but Louis' Schmeling-Charles streak pisses all over Marciano's win streak.
Great pick, but I think Robinson's competition edged out Tunney's. The biggest name there is obviously Greb, who was out of his depth against Tunney in terms of size (a win on his behalf is clearly a credit to his ability), and Dempsey was obviously past his best. Still, a brilliant streak.
Probably Chavez, up to Pea he always found a way to win. I count the Draw against Pea as the first 'loss' as everyone knows it was a gift.
Felix Trinidad was a good run He went around 40-0 Unfied IBF / WBC World Welterweight Titles Unfied IBF / WBA World Light Middleweight Titles Wan WBA World Middleweight Title Very successful undefeated career to that point
Carlos Zarate's record is pretty impressive: 52-0 at the start of his career, and a whopping 51 KO's in that run. The level of competition has to be questioned though.