You know who else has excellent vibrato - John Sykes (I was just listening to Blue Murder yesterday and it was one of the things that caught my attention). I'm also surprised no one has mentioned the flawless vibrato of Yngwie J. Malmsteen - despite being a complete douche - he has great vibrato.
I love his videos and what he says, but sometimes fast vibratos are better than slow vibratos.
http://dl.dropbox.com/u/332050/Vibrato eg.mp3
To be honest, I never thought about it until now, but I guess I would say I always do half step vibrato when the pitch I'm centered on is the one I'm fretting, and whole-step vibrato when the pitch I'm centered on is the one I'm bending to (in other words, notice how it sounds like I'm focused on the higher note in the second half, unlike in the first)
I just incessantly studied Malmsteen and Mike Akerfeldt. Whatever they did felt 'correct' enough for me to emulate.
There have been some great suggestions here.
The Leper Affinity solo, without a doubt.
I also like the Amott brothers, Mike has a nice control of fast/ wide vs slow/ shallow, but I think Chris has a nicer phrasing of it with better pitch control. Actually I like Chris over Mike in general.
Chris " Gathering of the Storm" Solo : http://dl.dropbox.com/u/341581/01 Gathering Of The Storm.mp3
A PURE FUCKING EARGASM!