men:
the late John Hartford
Leonard Cohen
...and, of course, Murray MacLeod! ¤;-D
 

for women (in addition to Emmylou, Joan, Tish, etc.:
Alison Krauss
and Marti Seidell (of The Dixie Chicks)  [ Even though the Chicks are commercial C/W artists, a lot of their stuff is pure bluegrass, BTW.]
 
 

And of the Mudcatters I've seen pictured, I'd say Carol C. (now "Carol The Sailor?") would be right up there.

Genie

PS., Someone mentioned above that the sexiest folks may be someone who's pretty much unknown.  My vote would be for a guy named Doug who lives in Seattle, plays 12-string and autoharp (both beautifully), is about 6'2" or so, sounds like Marty Robbins, does a lot of Kate Wolf songs, and is gorgeous.  I'd wager you folks probably know a few unknown folksingers in your local communities who'd also get lots of votes if they were more widely known.