I want to go everywhere! Only been to about 25 countries so far, so I have a long way to go - and it gets harder as you get older!
I take it you're from the USA? For a nearby vacation Canada and Mexico (the safe bits, like Yucatan peninsula) have some amazing experiences to offer. South America too. Haven't been to Machu Pichu yet, but it and Argentina are both high on my MUST SEE list.
More obscure - try diving off the 2nd largest barrier reef in the world - Caye Kulker off Belize. Stunning.
More close by - if you haven't been to Yosemite, Yellowstone, Grand Canyon, Zion Canyon, Bryce Canyon, Arches NP, Canyonlands and Monument Valley yet then you've missed the best bits of the states.
/edit - My next goal is Ankor Wat (however it's spelled!)