Six Flags parks have had a decades-long promotion with Coca-Cola during which you can redeem specially marked cans of the soft drink for discounted tickets -- often for as much as $20 off a single-day ticket -- which can be used most operating days. You'll often save a similar amount by buying tickets on the Six Flags website.
You can buy a season pass via the Six Flags website, which provides unlimited visits for the price of a single-day ticket. You'll also score other freebies such as free tickets for friends and in-park discounts. Purchase at least 15 tickets online and you get a group discount. Members of the military don't get a deal at the door, but discounted tickets frequently are available at their posts.
All of the Six Flags parks offer discounted tickets for people under 48 inches tall as they won't be able to enjoy all of the rides because of height restrictions and free tickets for children under age 2.