There are tons of good ones. I often rent from timeshare owners on sites like TUG2.net and Redweek.com.
Some we've done recently and really liked are Cypress Pointe and Cypress Point Grandvillas (the second bedroom in these is small, but they have tons of three bedrooms and that's what you would need), Sheraton Vistana resort (mostly two bedrooms, but they are lovely units (rencently remodeled) and sleep eight with the sleeper sofa), and Orange Lake. All of these resorts have lovely ammenities -- pools, tennis courts, some activities, etc.
If you need more than three bedrooms, you might want to do a home rental. Other posters could give you advice on that.
Orlando is wonderful for offsite accomodations -- so many great places at very affordable prices. The area has always been overbuilt and had great deals. I can find better deals here on accomodations than any other place I've ever visited when looking at quality for the price.
