Making your own flavored water is really easy! You just need a pitcher full of water, and some fresh fruit or vegetables. I've soaked a lot of different fruits (and veggies) in my water: blueberries, strawberries, oranges, lemons, lime, and cucumber. After you add your fruit or fruits (combining multiple fruits is both fun and tasty), refrigerate the water for a few hours to let the fruit flavor blend into the water, and then you are good to go until the pitcher runs out, at which point you can usually add more water to the same set of fruit (if you drank the water quickly).
If you are too busy to make your own naturally flavored water, I have to say Hint water is a very close substitute. The fruit flavor is very subtle, but yummy enough to help me easily drink my 8 cups of water per day. I really like drinking Hint water when it is refrigerated versus warm. Hint water comes in a ton of flavors (you can check out the Hint website to see a complete list) of which my personal favorites are pear and strawberry kiwi.
You can buy fruits and a pitcher for making your own water at almost any grocery store. You can buy Hint water at Whole Foods (with the refrigerated drinks) as well as at Jamba Juice, and at the Yummy Diet Food Amazon Store.
What fruits do you like to put in your water?