How about taking a trip to the toy store, and letting them each pick out any board game they want (no toys, video games, or anything else).
You can announce that you are going to have board game night from time to time (or card game night), and then tell them they each can pick one or two new board or card games.
I agree with the other reply about no video or TV during that night. They may complain at first, but I bet they will come around, especially if they help pick out the games.
My husband and I love board games, but it's always so much fun to pick out one we haven't played before.