Before visiting a new city or a country, I always make it a point to see the website, Happy Cow.
Happy Cow is a great website, it lists all the vegetarian and vegan restaurants in a city.
You can find vegetarian and vegan restaurants from Australia to North America and Africa to South America.
Here is another interesting website for people interested in plant-based eating, http://veganbackpacker.com/
Youtube is another wonderful resource for Vegetarians and Vegans.