At least a year since I've seen an episode. Longer -- 2? 3? 5? since I considered myself part of the fandom.
Susan Foreman -- Carole Ann Ford
Ian Chesterton -- William Russell
Barbara Wright -- Jacqueline Hill
Vicki (no surname) -- Maureen O'Brien
Steven Taylor -- Peter Purves
Katarina (no surname) -- Adrienne Hill
Sara Kingdom (possibly not an official companion; still debated) -- Jean Marsh
Dodo (Dorothea) Chaplet -- Jackie Lane
Ben Jackson -- Michael Craze
Polly (no surname given; fanwank ascribes it as Wright from casting sheet type things, or Lopez from...er...fanwank) -- Anneke Wills
Jamie (James Robert) MacCrimmon -- Frazer Hines
Zoe Herriot -- Wendy Padbury
Brigadier Alastair Gordon Lethbridge-Stewart -- Nicholas Courtney
Sargeant (later Sargeant-Major) Benton (possibly John) -- John Levene
Captain Mike Yates -- (arrgh...um..er...do I get to not count him because he's UNIT staff and not an official companion? Huh? Please? That way he won't break my streak.)
Dr. Liz (Elizabeth) Shaw -- Caroline Johns
Jo (Josephine) Grant -- Katy Manning
Sarah Jane Smith -- Elisabeth Sladen
Harry Sullivan -- Ian Marter
Leela (no surname) -- Louise Jameson
K-9 (Mk.1) -- John Leeson
K-9 (Mk.2) -- John Leeson (and David Brierly)
Romana (Romanadvoratrelundar, aka Fred)-- Mary Tamm and Lalla Ward
Adric (no surname)-- Matthew Waterhouse
Nyssa (no surname, unless you count "of Traken") -- Sarah Sutton
Tegan Jovenka -- Janet Fielding
Turlough (Jr. Ensign Commander Vislor Turlough) -- Mark Strickson
Kamelion (though boo, hiss, for storing a companion in the utility closet until they could conveniently kill him off, because his FX cost too much.)-- Gerald Flood (voice of, plus whichever actors he impersonated)
Peri (Perpugilliam) Brown -- Nicola (shudder) Bryant
Mel (Melanie) Bush -- Bonnie Langford
Ace (Dorothy, no surname given in series, given as McShane in followup novels) -- Sophie Aldred
Professor Benny (Bernice) Summerfield
Chris Cwej (should be pronounced Schvey, he pronounces it Kwedge because he's given up on other people getting it right)
Roz (Rosalyn) Forrester (okay, she has a longer family name, but I count myself as beat on that one)
(fic only, no actors, except for Lisa Bowerman who does Benny's voice in the NA plays, and you just didn't want to know that I knew that, did you?)
And the buck stops at the end of the New Adventures, even though I did buy and read the first 10 or so BBC novels. Sam who?
Sigh. Dr. Grace Holloway, whose actor I have mercifully blanked from my memory. Go 'way Bad Lady Who Kissed the Doctor.
How sad am I?
edited to add: Very sad. Mike Yates was played by Richard Franklin. No, I didn't look it up, or peek at comments. I just remembered it in between my alarm going off this morning and actually getting out of bed.