Depending on the passport you hold, it can be a breeze to visit another country, or it can be a maddening process that takes months of paperwork, clearance, visits to consulates or embassies and the risk of getting denied anyway. Passport Map can help you figure out what you're in for before you plan a trip. Passport Map is a fun enough site in its own right, since you can explore the passports of various countries on the main page, but its real value is in the visa comparison table, where you can select the country you hold a passport with, and see what the entry and visa process is like for virtually every other country on the planet. You can even add multiple passports to the comparison list, so you can see how, for example, your Kiwi friend would fare if you travelled together, or just what it might be like to be a tourist from another country.
If you prefer, click the "compare by destination" tab to see what specific countries put visitors from other nations through if they want to visit. Sadly the site doesn't help you jump off to visa information for those countries, or even to the embassies for the countries that require them, but it's a good starting point for your research if, for example, you're an Australian looking to visit China, or a New Zealander who'd like to visit Ghana, in which both cases a visa is required.