Like Eternal Padawan said somewhere else, anything by Burl Ives. I can't think of a single non-Christmas song he did, but everyone knows his Christmas stuff.
The entire "White Christmas" CD by Elvis, which collects all the Christmas recordings he ever released on one disc. Best of all are Blue Christmas, Santa Claus Is Back in Town, and his takes on White Christmas, O Little Town of Bethlehem, and Silver Bells.
Any Christmas recording by U2 (they covered Happy X-Mas? really? I gotta find that!) or Bruce Springsteen. Both of them should release Christmas albums.
The classic Motown albums by Stevie Wonder, the Temptations, and the Jackson 5.
All of Merry Axemas: A Guitar Superstar Christmas and most of Merry Axemas 2. (Joe Perry tearing through Blue Christmas is super-classic.)
The soundtracks to Home Alone, Home Alone 2, A Charlie Brown Christmas, and The Nightmare Before Christmas.
Most of the stuff from the A Very Special Christmas CDs. (Though there's always some bad fluff on there.)
Run Run Rudolph by Chuck Berry, Santa Claus by Sonny Boy Williamson II, and BB King's A Christmas Celebration of hope. There's not a whole lot of Christmas blues out there.
Songs by Tony Bennett, Frank Sinatra, Dean Martin, Nat King Cole, Bing Crosby, and other folks I think are great singers but don't often listen to.
Other stuff slipping my mind.