Hilton Bonnet Creek & Waldorf Astoria Bonnet Creek are offsite hotels located on Disney property, and share a big pool complex complete with waterslide and lazy river. They also provide a free shuttle to and from the theme parks.
Four Seasons Orlando has an even better pool complex, but is uber expensive.
Waldorf Astoria Orlando: Standard pool but adjacent to Hilton Bonnet Creek with full access to their pool. (Sometimes the Waldorf Astoria is cheaper, which is why I'm adding it here.) Link: http://www.waldorfastoriaorlando.com/