How to flavour iced green tea?
Have you tried using one green tea bag and one bag of herbal tea? There are many herbal tea sampler packs that you could get to try several flavors of tea. Since you are making iced tea, I would also recommend adding chopped fruit once the tea has chilled - I would imagine some crisp apples or even a fresh melon would add a really refreshing profile. You can even let the fruits steep in the chilled liquid, like a tea-sangria.

Another option is to create a flavored simple syrup in order to sweeten your iced tea. It's always better to use a simple syrup in a cold liquid than any kind of 'dry' sugar. Simple syrup is easy to make on the stove or in the microwave, and just add some flavors you might like while heating it. I wouldn't recommend vanilla for green tea (gut reaction), but maybe lavender, orange or cardamom?