My first recommendation is Josh Groban's NOEL. The entire album is rich and warm but "Thankful" is really my favorite. I just used it as the background music for a little video I made of my son.
I also love Faith Hill's new song, "Little Drummer Boy." She sang it so beautifully at the lighting of the Christmas Tree in Rockefeller Center in New York City. She had a choir behind her and it was so touching.
Mariah Carey and Frank Sinatra both have fantastic Christmas Albums out that are perfect for parties. Tony Bennet's new release, "A Swinging Christmas," is a great party album as well.
When my family comes over on Christmas Eve I am going to play "What Child is This?" by Kristin Chenoweth, "Hark the Herald Angels Sing" by Straight No Chaser, and Sarah Brightman's "A Winter Symphony." All of these are new releases for 2008 and I can't wait to add them to our playlist from last year.
For something with a little more of a folk touch I like "Coventry Carol" by Gretchen Peters or "Emmanuel" by Loreena McKennitt.
Have fun Caroling!