As they often go to Wales to film, there are probably plenty of them. Eve Myles, who played the maid, Gwyneth, in "The Unquiet Dead" and went on to play Gwen Cooper of Torchwood, is most definitely Welsh, so, she's one example.
Out of all the actors who have played Doctor Who only 3 of them have died. Those 3 are: William Hartnell, Patrick Troughton and Jon Pertwee.
Which ones- do you mean just the actors who played The Doctor, or are you including his companions and other major stars from the series? You need to try and narrow down your question before it can be answered.
Sylvester McCoy, the Seventh Doctor, and David Tennant, the Tenth Doctor, are the only Scottish actors to have "officially" played the Doctor, though many companions and side-characters have been Scottish. UPDATE: As of 2014, Peter Capaldi has taken on the role of the Twelfth Doctor becoming the third Scottish actor to "officially" play the Doctor.
The cast of Doctor DeSoto - 1984 includes: Ian Thomson as Narrator
Milton Welsh is 180 cm.
No
Meddyg
The cast of Sounds from the One I Love - 2008 includes: Cody Lightning as Melvin Hollis Welsh as The Doctor
There was Dafydd Williams who was a Welsh-Canadian.
According to online translators, mountain ash is Aberpennar, in Welsh. (I stand to be corrected by any Welsh speakers!.)
You could do about the history of the Celts or Welsh princes, the castles or lanscape, or famous Welsh people and artists/singers/actors.
The cast of The Story of Welsh - 2003 includes: Huw Edwards as Himself - Presenter
There isn't any specific regions in Wales where there are Welsh speakers as there are Welsh speakers all over Wales.
The cast of Rolf on Welsh Art - 2011 includes: Rolf Harris as himself
The cast of The Welsh Great Escape - 2003 includes: Jack Davenport as Narrator
Katherine Jenkins.
You can find Welsh people in practically any country.