For all around jaw dropping leather work Peter Main is of course on my list.
As far as knife sheaths go Sandy Morrisey, Paul Long, Gary Graley, David Abramson(http://www.liftersleather.com), Dwayne Puckett (http://www.armoralleather.com), Dave Cole(who is a member here), and Kenny Rowe(http://www.rowesleather.com) do the kind of work I aspire to. Not only do all of these gentleman do fine sheath work they are generous with their knowledge as well.
As far as western/saddle work there are too many folks on this board to mention. Although when I think I would like to try builing a saddle I think of the saddle Troy West built for President Bush, as the gold standard.
I really want to take up boot making. So I would have to say that D.W. Frommer and Carl Chappel come to mind as inspiration.