So, you are anywhere from just out of high school, in college, or a recent graduate (recent can be stretched a few years) and with an economy and job market in the pits, it is important to be frugal and let's be honest, it can be very difficult to have a good time without spending money. However, I actually have an easy solution for you; Go Outside. Thanks to historical figures such as Theodore Roosevelt and John Muir (the father of the National Parks) and more recent help from organizations like the Sierra Club, we are actually lucky enough to have outdoor recreation opportunities all around us that are either free (because of taxes), or will cost you only a few dollars (the money usually goes towards park improvements). Go online to the National Park Service Park Finder or check out L.L. Bean's Park Finder to find National and State Parks close to your location.
However, if you happen to be in school, specifically at a public university, chances are your school offers some great outdoor opportunities to you for free, the caveat being you have to show them a student ID. For example, the University of Florida has facilities on Lake Wauburg and offers students, faculty, and staff everything from kayak and canoe rentals, a Frisbee golf course, mountain bike rentals (with a trail to boot), and even a massive climbing wall that will challenge you both mentally and physically. Just search your school's website for the recreation section, usually found paired with your gyms and intramural sports.
Next time you are being lazy and just mindlessly browsing the web, check some of the above resources and next time you start feeling like you need some fun; step outside, take a breath of fresh air, and have a good time at a low cost in The Great Outdoors.
Here is a picture of University of Florida's Lake Wauburg: