Never become your parents - there's a reason we all end up resenting them!
New York City - I know, how cliched? But New York City is a cliche for a reason. The city is moving 24/7. Jetlagged and bouncing off the walls at 4am? Why not travel to Times Square which is still all lit up and bussling with people. The Metro system is extensive and relatively cheap compared to a lot of cities so where you pay through the nose for things like accommodation, you save on travel expenses. Central Park is, well, CENTRAL PARK. The focal point in every romantic movie has a darker side when walking past the local homeless people living under the bridges but the park itself is beautiful and a nice escape from the cement and steel cladded buildings in a nice and "central" location.
Mexico City - When you tell people you are off to Mexico, the general response you get is either "So you're going to party it up in Tijuana?" or "I hear Cancun has mad beaches". Whilst i've been to both Tijuana and Cancun, i've found that Mexico City is a cultural hub and one of my favourite places in this world! The European influence of the city's architecture, mixed with the friendly and wealth motivated citizens add to the appeal of the city. Take a coach or train 30 minutes out of the Zocalo and you have Aztec Ruins, Teotihuacan.
The best thing about Mexico City - The People! The locals arn't just about ripping tourists off (although this a certain level of this should be expected), they love to educate you about the mixed culture and rich history of their city. There are also a lot of itinerant workers that come to live in Mexico City for one to three years for work. Backpackers flock there as it is the gateway to most flights through central America. One small city = Endless opportunities.
Penang (Malaysia) - Penang brings beach and shopping together to form a perfect tourist destination. Whilst i wouldn't recommend walking around after dark as a single person, the daytime in or out of the tourist district brings forth a safe feeling. Anything you could possibly want or need is on offer in the street markets (and sometimes even brought directly to you on the beaches). Penang has a little more class than going to Phuket or Bali whilst maintaining that "i'm a tourist and i'm here to relax, shop and drink all night long!"