I came up with an idea for remembering those friends and families you wish to send a Christmas card to every year. In your address book, using a red or green marker, place a "C" for Christmas next to last name of each person you wish to have on your Christmas list. This can easily been done even if you have your list on a PDA or computerized.
To further that, I write in pencil the year with a circle around it. It can be really small but then you can see who you wrote to last year (even those last minute ones when you receive one!)