Clapton has one of the best slow vibratos, BB King has the best fast and Kirk Hammett (and I'm a huge Metallica fan) has one of the worst IMHO.
I'd have to throw Beck in there as well. But he's so frickin' unconventional that its not really the one bit of his playing that stands out if you know what I mean.
i'll add Kossoff
finding guys with nice vibrato is easy. i'll bet most of us could identify a player from one note with added vibrato. think Tony Iommi when he bends a string...note goes up...fast vibrato...vibrato stops...note comes back down. i could spot him in a heartbeat. same with all the other guys mentioned here.
what would be more interesting is doing a list of guys who are "famous" or "successful" but have bad vibrato....
The opposite of Hammett.