I married into a Disney family from Florida. They have a time share there so we have the luxury of visiting and staying at Disney for "free". Although we have this nice benefit, it has also been fun to experience Disney World from a frequent traveler perspective. My in-laws have stayed at all the resorts for years and have done it all. So what do we like to do for fun and FREE as we spend a week a year there to keep things interesting? (We also have park hopper passes and you can get those in multi-day increments that don't expire - it's recommended)
5) Walk the Disney Boardwalk, especially at night. It is just like the Jersey Coast. Games, taffy, people walking, noises, it can't get better than that unless you are at the real Shore.
4) Swim in the Yacht & Beach Club sand bottom pool. It is stricter now with wrist bands, but go after 5 and in the off season and you shouldn't have a problem. The water slide rocks!
3) Visit the Wilderness Lodge. Walk around the coolest real life Lincoln Logs building I've ever seen.
2) Ride the boats. From the park to resorts, from resorts to Marketplace village. Wherever. Free boat rides!
1) Take the monorail and do your own resort tour. Ride the monorail and visit each resort on it. Experience Hawaii at the Polynesian. Visit the gameroom at the Contemporary. Breathe in the splendor of the fresh flowers in the entrance of the amazing Grand Floridian. Ride in the front car and learn from the driver all about Disney.
There is so much to do and see there. It really is nicer when you stay on site. And a great place on a budget is the All Star Resorts.
Official Web Site
Disney Tips, Discounts
More free and cheap things to do at Disney World