In no particular order:
Drive to Alaska, stay in Anchorage and have side trips to Kenai Peninsula, Valdez, drive the Dalton, walk on a glacier, see Northern Lights. Live in Fairbanks and go down steep ice slides with kids. Costs: Made money (wife had travel nurse contact).
Climb Chichen Itza, Altun Ha, and other Mayan pyramids. Cost: Maybe a couple thousand (portion of various cruises, hard to separate out).
Cave tubing in Belize. Cost: Hundreds (cruise)
Visit castles in Spain and Portugal. Cost: Thousands (Trans-Atlantic cruise).
Visit China, see Great Wall*. Cost: Free (had day layover in Beijing).
Visit Hong Kong. Cost: Thousands.
Live in Australia. Visit all the states/territories*, Uluru*, Sydney, see crocodiles in the wild, pet kangaroos, hold koala, visit Great Barrier Reef. Cost to live in Australia: Making money (wife works as midwife here). Additional cost of aforementioned side trips: Thousands (probably over $5k...of course we spent more but I'm trying to separate costs for those things listed).
Visit both New Zealand islands. Cost: Thousands (over 5k for one cruise, close to $1k for a short 2 day trip prior).
Cross country trip stopping at Las Vegas and Grand Canyon. Cost: Free (cost less to drive than fly, ended up buying car in California and selling for a profit in Tennessee). Note that we only had time for breakfast in Vegas and saw Grand Canyon just after sunset, so trip may be repeated (family emergency, had to shorten trip).
Live in England*
African Safari*
Egyptian pyramids*
Antarctica*
Live on boat*, cruise rivers in Eastern US*, cruise Bahamas*
Space**
* - Things I have yet to do, but fully intend to.
** - Probably not going to happen.