Coke Zero is putting out a coupon for $0.99 off of a Coke Zero with no size restrictions. I know a lot of the couponing sites out there are listing it saying that you can buy a 20 oz. with that, but a lot of the stores around here mark their 20 oz. beverages at about $1.50. I noticed, however, while at Weis the other night that 1 liter Coke Zero is in their "seasonal" section listed at $0.99, which would make it free. Or you can print it and wait for a Coke sale and get a 2 liter for free instead.
All you have to do is go to Coke Zero's Facebook Page and "like" them. Then go to their "Trial" page and you'll find the coupon. I was able to print two before getting a message that I had printed the max number of copies.
Good luck and happy couponing. :-)