Czech and I have duked the halls over this before, but I have to go with the original Manhymen Steamroller Christmas album, especially for the analog-synth laden nostalgia inducers that are "Deck the Halls" and "Good King Wenceslas."  Oh, and A Very Special Christmas is another favorite for bringing back those late 80's/early 90's memories. 
  
As for "Do They Know Its Christmas?", I mostly just remember it for kicking off the trio of international charity songs.  I thought it was bleh, though not as atrocious as "We Are the World".  Canada won that one easily with "Tears Are Not Enough"... that would be discussion for another thread though