Off the top of my head (sorry if they have been mentioned) and in no order of preference...
Peter Dinklage
Kate Mulgrew
Robert Picardo
Nathan Fillion
Michael Dorn
Brent Spiner
Paul Darrow
Jacqueline Pearce
Gareth Thomas
Brian Blessed
Robert Englund
Michael Gambon
Robbie Coltrane
Lance Henriksen