The pre-DW Hartnell role that intrigues me is always Hell Drivers. In addition to a pre-DW Hartnell, it has a pre-Prisoner/ Danger Man Patrick McGoohan, a pre-007 Sean Connery, a pre-Professionals Gordon Jackson and a pre-Man from UNCLE David McCallum. In addition to having Jill Ireland, who was Spock's love Leila in Star Trek's This Side of Paradise (and who would marry McCallum and later Charles Bronson), it also features Herbert Lom (Dreyfuss in the Pink Panther films) and British comedy legends Sid James and Alfie Bass.
Troughton was the priest impaled in the original The Omen. He was making a movie called the Viking Queen when he got the news he was the new Doctor.