To echo Scarfman's comment from the Mac side (and the PC side, from what I understand), VLC is a little miracle-worker. I use it to play everything these days. It plays damn near everything without you having to hunt up extra codecs (which is how QuickTime operates, alas) and it also ignores region coding, at least on the Mac, so it's got that extra advantage.

I loved "The MInd Robber" and "The Invasion"--and "The War Games is also fabulous. I really should scrounge up a Troughton icon one of these days...