Huffington Post has an article going around about the 50 cities you should see in your lifetime. The article can be found here.
So, let's see what my total is:
1. Venice, Italy (check)
2. Seville, Spain (check)
3. New York City, New York, USA (check)
4. Lhasa, China
5. Rio de Janeiro, Brazil
6. London, England (check) also planning our second trip there for the Miami Dolphins game
7. Marrakech, Morocco
8. Petra, Jordan
9. Rome, Italy (check)
10. Varanasi, India
11. Florence, Italy (check) loved it, highly recommend a visit
12. Havana, Cuba
13. Kyoto, Japan
14. Jerusalem, Israel
15. Paris, France (check, multiple times)
16. Beijing, China
17. Lalibela, Ethiopia
18. Granada, Spain (check)
19. Athens, Greece (check)
20. Bagan, Myanmar
21. Kathmandu, Nepal
22. Vatican City (check) would love to go back, same goes for Rome too!
23. Lisbon, Portugal - will be our last trip before we move back to America
24. Tokyo, Japan
25. Istanbul, Turkey (check) amazing!!!!
26. Hoi An, Vietnam
27. Amsterdam, Netherlands (check)
28. Luxor, Egypt
29. Berlin, Germany (check)
30. Jaipur, India
31. Lyon, France
32. Oia, Greece
33. Siem Reap, Cambodia
34. Vienna, Austria (check)
35. Cusco, Peru
36. Cartagena, Colombia
37. Zanzibar, Tanzania
38. Mexico City, Mexico
39. Singapore
40. Las Vegas, Nevada, USA (check)
41. Samarkand, Uzbekistan
42. Sydney, Australia
43. San Francisco, California, USA
44. Mont Saint Michel, France (check) stunning
45. Dubrovnik, Croatia (check)
46. Bangkok, Thailand
47. Buenos Aires, Argentina
48. Antigua Guatemala, Guatemala
49. Prague, Czech Republic (check)
50. Budapest, Hungary - hoping to visit before we leave
So, I'm at 18 for now. We'll see how many more we can add before moving.