My list seems to show a bias to the western world:
1. Alhambra
2. Big Ben
3. Brandenburg Gate (easy one; I see it every other week)
4. Broadway
5. Eiffel Tower
6. Leaning Tower of Pisa
7. Louvre
8. Neuschwanstein
9. Notre Dame
10. Parthenon
11. Prora (Hey, first one to list this! I wonder why....)
12. Pyramids
13. Sistine Chapel (well, at least the incredible long queue in front of it; I decided to limit myself to St. Peter instead.)
14. Statue of Liberty
15. Statue of Zeus (the rest of it; which is few enough.)
16. Uffizi (from the outside. Does this count?)
(17. Circus Maximus; I mean the C.M. in Rome)
(18. Here should be the Hagia Sophia. I still can not belive that I was in Istanbul and didn't visit it. Well, I'll change this in the not so far future. I promise!)