From my experience, here's a short list of places I've seen with my own eyes that are a MUST before you die:
1) San Juan Islands - WA, USA
Chain of over 200 glacially-carved islands with caves, forests, tide pools, schools of Orca whales and seabirds, and a unique Mediterranean climate between Washington and Canada.
2) Santa Cruz - CA, USA
In my opinion the most beautiful stretch of CA coastline you'll ever see.
3) New York City - in terms of pure urban energy and amazing architecture, I think New York has no equal anywhere else.
4) Cahuita, Costa Rica - for amazing, laid-back tropical beaches and good cerveza, it doesn't get any better than this.
5) San Francisco, CA - especially Golden Gate Park, Twin Peaks, Castro, and the North Beach area, spending a few days/weeks here may change your life forever. One of the most vibrant cities I've ever been in.
6) Barcelona, Spain - Similar culturally and geographically to San Francisco, but in a European context. The nightlife here can't be beat! The nearby Costa Brava to the north is also worth a road trip.
7) Cadiz, Spain - one of the best Carnaval celebrations in the world, year-round sunshine, great seafood, and the best beaches in Europe.
Fes, Morocco - a fascinating medieval market that stretches for miles, and some of the richest and most delightful food I've ever had.
9) Tel Aviv, Israel - one of the most underrated beach destinations in the world, round the clock nightlife, and of course a city full of hip beautiful Israeli men! The face of modern Israel.
10) Amsterdam - canals, bikes, legal drugs, and spectacular city planning - the Dutch did this one right!
Places I have yet to see, but are on my bucket list:
1) Rio de Janeiro and Salvador, Brazil
2) Buenos Aires
3) Bogota, Colombia
4) Mexico City
6) Italy - especially Rome, Naples, and Florence
7) London, UK
9) India - would love to see Mumbai and Goa