Yosemite National Park
It's no secret that national parks are a pretty cheap date, vacation-wise. But few parks can match the natural beauty of Yosemite. For avid hikers, Yosemite has some of the best trails around, but even a leisurely stroll on the valley floor is something to write home about. Older kids will enjoy the Ansel Adams Gallery (free), which features the iconic photographer's work in Yosemite, while younger kids will have fun exploring the bark tepees in the replica of the Indian Village of Ahwahnee behind the Yosemite Museum (free). While there are more rugged (and cheaper) camping options, you can't beat the Wawona Hotel (rooms starting at $77) for its blend of amenities, value and, well, solid walls.
One of Canada's biggest cities, Vancouver isn't your typical tourist-trap town. Setting up base at the affordable Pan Pacific (rooms starting at $129) puts you within spitting distance of the hip Historic Gastown District (free), Vancouver's oldest neighborhood. With a free two-story play area inside and water park (open in summer) outdoors, the Kids Market will entertain children for hours. Finally, take a walk on the wild side over the Lynn Canyon Suspension Bridge (free) or splurge on the Capilano Suspension Bridge and Treetops Adventure, a series of bridges through the tree canopy ($32.95 for adults, $21.95 for kids 13-16, $12 for kids 6-12, and free for kids under 12).
Washington, DC, is loaded with free museums and landmarks, many within walking distance of each other. Go for a hotel near the National Mall: The money you save in transportation will add up quickly. The State Plaza Hotel (rooms starting at $90) hits it out of the park for value and location. As for sights, the 19 museums that are part of the Smithsonian Institution are all free, so hit as many as you can. Two can't-misses: the National Zoo and the National Air & Space Museum.
Yellowstone National Park
A geyser that shoots water jets over 150 feet high, Old Faithful (free) is the Yellowstone classic, but you'll also want to catch the Fountain Paint Pots (free), pools featuring a dazzling array of colors formed by water bubbling up through the rock. As for bunking, you can go the cabin route if you're feeling woodsy, but otherwise, try the Old Faithful Inn (rooms starting at only $58).
Taking a Caribbean vacation on the cheap might not sound possible, but Paradise Island is just one of those impossible places. With pristine beaches and crystal-blue waters, the whole island is a natural (and free!) attraction. If you make a day trip to Nassau, stop at the Pirates of Nassau museum ($12 for adults, $6 for kids) to see displays depicting the real pirates of the Caribbean. Stay at (rooms starting at $110), an all-suite property with (wait for it) free access to the neighboring Atlantis Resort's world-class water park.