While buying bottled ice tea is a viable option, it's more fun and economical to make use of the wide varieties of tea you probably already own like chai, jasmine, darjeeling, and oolong. The flavor options are limitless, and you'll notice that most teas have a slightly more robust flavor when chilled.
To transform your hot tea collection into refreshing iced tea, brew the tea as usual, then chill it in the fridge. For every cup of filtered water, use one teabag (or two teaspoons loose-leaf) of any black, green, white, or herbal tea variety. Remove the teabags after three to five minutes of brewing, and allow the tea to come to room temperature before popping it in the fridge.
For a faster cup of iced tea, make a "condensed" tea by brewing two or three teabags per cup of filtered water. Then pour the hot tea directly over ice. If you don't even want to mess with hot water, there's also a way to cold-brew tea! Once you've made your unsweetened iced tea, it will generally last about three days in the fridge - that is, if you don't drink it before then!