Many unguessed lyrics below. This was a busy weekend for many of whom I assumed were regular readers, so I'll wait until the weekend to complain bitterly about low participation and start pulling links from the sidebar post answers. I think the only obscure songs are 2, 16, and 18. Okay, 20, too. The others are fairly well known. 10 and 11 were featured in major ad campaigns; 11 in particular seemed ubiquitous during the holiday season.