Pernell Whitaker, Manny Pacquiao, Mark Too Sharp Johnson, and Vasyl Lomachenko put together some really nice combinations.
Sergio Martinez and Cory Spinks come to mind as more recent fighters. I live in St Louis and saw Cory fight quite a bit when he was coming up. Super fast hands especially when he was an amateur. He used to just overwhelm guys. Became much more defensive as a pro but could still let the combos fly.
Saldivar was the best southpaw combination puncher. Look no further than the Sugar Ramos fight for proof. Second I would say Too Sharp Johnson, awesome combo puncher.
Glad to see Gushiken get mentioned. Although he doesn't seem to be held in as high regard as he used to be, he was a very good combination puncher and a difficult matchup for any JFly.