Copper is the most common element used to cause a green flame ! You can also use chemicals to achieve a green flame : 
Green flame is possibly the coolest color to turn flames. It's not a color you get from the fuel, so you have to add a chemical to get the effect. The color comes from the ion emission spectra, so you can use any of the chemicals that produce green in the analytical method known as the flame test. The most readily available compounds are: 
boric acid (boron compounds), sold as a disinfectant and roach killer
borax (boron compounds), sold as a laundry booster and home cleaner
copper sulfate (copper(II) compounds), sold as a root killer and algicide
However, other chemicals will make green flames:
thallium compounds
antimony compounds
barium compounds
manganese (II) compounds
molybdenum compounds
ammonium compounds
phosphates moistened with sulfuric acid