+1 for Amsterdam.
I have never been myself but have heard wonderful things about Singapore.
I went to Madrid last December by myself and really enjoyed the city. Not speaking Spanish was a bit difficult but I could eventually come across people who did. The males were fairly aggressive with expressing interest... This could be a positive or negative depending on what you are looking for on the trip.
My friend went to Dubai by herself and says it is one of the best trips she ever took.
If you want to stay a bit closer NYC is beautiful in November. Hotels are ridiculously affordable Thanksgiving week (at least they were last year and the year before).
This is such a great idea! I think I will steal it for when I turn 40!