RJJ had a great one, Cotto's and Margarito's aren't bad either. But I can't think of any of the top of my head.
I've not looked it up again but I seem to recall De La Hoya having an impressive start to his career, no fighters with bad losing records? I'll just re check... Edit: Yes, all fighters had winning records, won the WBO super featherweight title in his 12th fight, won the WBO lightweight title 2 fights later then in his 18th fight unified it with the IBF and beat 34 year old Julio Cesar Chavez in his 22nd pro fight. Not the kind of resume I'm used to seeing British prospects with after 22 fights... David Haye has done very well in that time too actually.