Only Floyd Mayweather & Sugar Ray Leonard have done it that I can think of. Manny Pacquiao will have done it if he beats Hatton & Winky Wright will have done it if he beats Paul Williams although he lost when he went up so may not really count. Not many others come to mind immediately. The thing with the two guys who've actually done it is that they were both technically skilled boxers fighting well above weights that were actually suited to them, & the same would be true of Pacquiao in that he really should not have been fighting as high as 147 size-wise.