Buy green tea and make it at home, either using teabags or loose leaves.
I drink three different kinda at the moment, a loose leaf one sweetened by the flowers 'Sweet Osmanthus' (IMO it doesn't make it sweet at all but that suits me), another loose leaf one called 'Gunpowder' (named because of the way they roll the leaf) and an organic bagged green tea.
You can sweeten it yourself using honey or a little sugar if you can't stand the bitter taste. Personally, I drink it unsweetened, but I like it that way.
You can also drink bagged green tea's that have flavours added, such as blueberry/pear etc (or at least you can buy it here in UK) and still get the health benefits from it. As for brands etc, I don't know what you can get over in Americaland, but I'm sure there will be a fair selection in any food store.
If you're drinking tea in a restaurant can't you ask them not to add sugar/sweeteners and then add it yourself? Here, we get the drink as it is without sugar and then can add it if we like, unless you're getting a flavoured drink that they use syrup for.
If you're interested in green tea for the health benefits it provides, but don't like the taste etc, you can always take green tea supplements, which has all the ''good stuff'' in a tablet. My mom takes them since she doesn't like the taste of the tea. But you should speak to your doctor etc before taking them (eventhough they're not harmful, I'm just reading that off the bottle :P)
You can also break the tablets and use the powder inside to make it into a tea, but I find the taste is really off, lol