I have enjoyed many Christmas books over the years -- The House Without a Christmas Tree. The Best Christmas Pageant Ever. The Gift of the Magi. A Christmas Carol. They're all great. But what I'm really, really a sucker for is lavish illustration and a cute story. So my very favorite is Jan Brett's The Wild Christmas Reindeer. It's about a little elf girl who is charged with prepping Santa's reindeer for the Christmas Eve voyage, but the reindeer don't want to cooperate. She learns how to be more patient and gentle, and the reindeer are ready on time.
I could look at the artwork in Jan Brett's books for hours. It's very Norwegian and colorful. There are all kinds of hidden details, including side panels featuring Hedgie the hedgehog looking for a cozy winter home or something like that. My son and I love Hedgie. Jan Brett visited his school when he was in kindergarten and gave all the kids a little beginning reader book about Hedgie.
Anyway, if you're looking for something to read with your kids for Christmas, Jan Brett's book are the best.