In no order:

Muhammad Ali - greatest of all time
Joe Calzaghe - exciting to watch, fast hands, amazing workrate, one of the best in his division ever
Ricky Hatton - exciting, devastating body attacks, unreal workrate
Bernard Hopkins - not really exciting but a brilliant fighter, beat the best in his division in his long reign
Naseem Hamed - cocky but entertaining, quality fighter
Marco Antonio Barrera - loads of heart, has showed us many great performances, legend
Oscar DeLaHoya - brilliant fighter, multi weight champ, great guy outside the ring, one of the best of the 90's
Roy Jones - Phenomonal speed and reflexes, beat the best over the years, multi weight champ
Lennox Lewis - cleared up the heavyweight division, beat all the best
Kostya Tszyu - unreal power, great champion, beat th best there was