The Corley fight really wasn't that close...people only say that cuz Floyd buzzed him pretty good...other than that Floyd whooped his ass...
It was a pretty exciting fight though, but Mayweather did really beat the shit out of him.
Jose Luis Castillo was his closest fight (the first one, although you get a nice contrast if you watch both)
Emmanuel Augustus is the guy that Floyd credits with being his toughest opponent
Some people say the Oscar fight was close although I disagree with that
Zab Judah and Demarcus Corley are the two fighters that tagged Floyd really good
Jesus Chavez was a real tough fight
Carlos Hernadez was the fight where Mayweather actually got knocked down, although it was him going down on his own from a hurt hand.
Philip N'Dou was a pretty good fight to watch