Hans Weilenmann - perfect flies every time; a master of thread control and proportions, never an extra thread wrap where it's not needed.
Davie McPhail - see above
Craig Mathews - quick, easy flies proven to catch fish in/around the Yellowstone area (where I do a lot of my fishing), and pretty much anywhere else you'd find trout.

These three are my favorites, but there are lots of other good tyers out there, as we'll.

Regards,
Scott