We have a gazillion - beetle, cards (snap), cluedo, guess who, game of life, battleship, jenga, a marble maze, chess, backgammon. We have monopoly (3 versions - gifts) but I despise it - it takes too long!
Cards are great for a heap of games, plus building card towers.
Also, not exactly a game, but I bought a bag of mini wooden paddlepop sticks and some glue, we have had hours of fun making xmas decorations, a barnyard and corral for plastic horses, houses, machines etc.