Here’s a great interactive graphic from Trulia.com that shows the ratio of renting to buying. The ratio is how many years of paying before you paid full price for an equivalent house. This data is comparing the median list price with that of a two bedroom apartment.
For example, in NYC renting is so much better that you’d pay rent for 39 years before you’d paid the amount the house costs. A good estimate is the rent-to-price ratio should be about 17:1.
The size of the circle shows how much the rent is (e.g. bigger circle means more rent). The color indicates the ratio (e.g. red means better to rent; green means better to own).