Even if you've never run in costume or with bells on your shoes (probably a good thing, since this would annoy most runners), a holiday race is the perfect time to try one of these ideas. In the Arthritis Foundation's series of Jingle Run/Walk events, for example, they encourage participants to tie jingle bells to their shoelaces. The sound of hundreds of jingling runners can definitely help get you into the holiday spirit. Some holiday races, such as the Las Vegas Great Santa Run, give each registrant a Santa suit to wear during the race.
Signing up for a holiday race is the perfect way to make sure you don't put your running on hold during the busy holiday season. Even if you don't have a Jingle Run/Walk or Santa race near you, there are lots of other holiday-themed races, so check sites such as Active.com for ones in your area.