Keep a jar with a certain amount of money (i.e. 10 bucks for every pound you want to lose this month), when you lose a pound, put $10 (or the amount you chose) into a glass money jar. If you don't meet your goal by the end of the month, donate the money left over to charity/give it to your spouse!
It sucks in the beginning because you may lose money, but it really does motivate you to stay on track. I have two jars, one for my ultimate goal weight, and one for my short terms... it helps!