It's still early in the day/week, but here are a couple of free themes to start off. The weekly PS Store update probably isn't done, and these technically aren't in the store yet (list dates are the 4th and 5th of January)—but no reason to wait, I guess. And don't forget to add the month's PS Plus games to your library, too.
The King of Fighters XIV: 'Athena Allstars' Theme
The King of Fighters XIV: 'Santa Girls' Theme