I too had a coke addiction, when I decided that I was going to lose weight I knew that it was going to have to be one of the first things to go.
I started off by replacing the coke with water, If I managed to be good all day water wise I would reward myself with one small glass of coke with my tea. That only lasted about 2 weeks.
One night I was drinking my nightly glass of coke and I couldn't finish it. It tasted sickly sweet. I haven't drank it since. So in almost 10 months I have gone from drinking 2-3 litres a day to drinking none at all.
Best of luck with kicking the coke