The Star Wars and James Bond films are also good places to find WHO related actors.
There's Peter Cushing (the Dr Who of the 1960s movies) in ANH for one. Funny enough, when pictures of Wayne Pygram as young Tarkin from ROTS first appeared online, aintitcoolnews. erroneously reported that it was Christopher Eccleston (pre DW).
I can also think of the late Michael Sheard from ESB, something of a stalwart of British TV shows including Who (no DW or SW character was ever as terrifying as his Mr Bronson in Grange Hill, though). More recently Hugh Quarshie was in TPM and Dr Who's Daleks in New York.
Colin Salmon from the Brosnan Bond movies was in DW's Library of the Dead. I also think that guy who played Rassilon in TEOT was in a couple of Bond movies ...
I always like to point out that Eccleston and current 007 Daniel Craig were in Our Friends in The North early in their careers. It also featured current villain du jour Mark Strong (Sherlock Holmes, Green Lantern - to be directed by Martin Campbell of Bond fame) in a leading role. Eccleston's movie debut Let Him Have It was written by Bond regular scribes Wade and Purves. And a pre-DW William Hartnell appeared in a movie called Hell Drivers with a pre-007 Sean Connery, a pre-Man From Uncle David McCallum and a pre-Danger Man/ The Prisoner Patrick McGoohan. McCallum also appeared alongside a pre-Who Tom Baker in a movie called Frankenstein: The True Story.
Patrick Troughton appeared as a priest in The Omen, which also featured David Warner, who has appeared in DW alternate media and quite a bit of Trek. GOing back to the original post (The Great Escape, Stalag), Troughton also appeared in the tv show Colditz.
Jon Pertwee was in One of Our Dinosaurs is Missing, as was Clive Revell, who played The Emperor in ESB and was for a while anyway, the only person to have appeared in Stars Trek and Wars. Oh, and Revill also hanged Eccleston in Let Him Have It (he played the real-life executioner Pierrepoint). Pertwee's last role was in Young Indiana Jones, in an ep which featured recent(ish) Who guest star Marc Warren, plus SW's Anthony Daniels.
Tom Baker played Rasputin in a 1960s movie, Nicholas and Alexandra which also featured recent DW guest star Brian Cox as Trotsky and Julian Glover, who has done lots of Who and some Bond.
David Tennant first came to prominence in Casanova, whose older self was played by Peter O'Toole, who was rumoured to be playing the Doctor's father during the 1990s, while the long-gestating movie was in development.
I'm officially Who-triviaed out.