Unsweetened Almond or Soy milk.
This stuff, especially the almond, is a kind is magic! The fat in the soy or almond gives you the unctuous taste of the fat, the health benefits are a plus and the light/unsweetened varieties are low calorie. I use it as creamer for my coffee, but this stuff is great as a swap for creamer in sauces, milk in scrambled eggs, and a nifty use in one of my healthy obsessions.
The boxed kind are also shelf-stable until you open them, so you don't have to worry about spoilage the moment you buy it. You can get the one in the dairy case, but I tend to prefer the box kind.
I learned about it from hungrygirl.com as she uses it in a ton of her recipes. I wasn't really amazed with it, it was also a pain to find at the time.
But, I became fond of it when I found it at Trader Joes (Trader Joes!) and gave up fat free half & half. The thing with FF Half & Half was I never used enough of it, and it would spoil. With the almond milk, the sheer volume difference in servings makes me love it. I was using 2-3 40-cal servings (2 tablespoons) of FF half & half everyday; the unsweetened almond breeze has the same amount of calories for a whole cup, and I don't use a cup's worth in day. I save money, calories, and get additional nutrients. That's why this is a must have for me.