Rental rates across the country have been falling pretty steadily since February. Nationally, the median rent for a one-bedroom apartment is down to $1,015 (a decline from January's median of $1,046). And while costs for two-bedroom units have been on the rise, May has also seen a decline in two-bedroom rates nationally. The median rent there is down 2 percent from January to $1,230.

Locally, a one-bedroom apartment will set you back about $1,227 a month. That's a 4.3 percent decrease since last month, when the same apartment would have cost $1,282. That swing makes Philadelphia the ninth most significant decrease in rental rates for May.

There are some markets where apartment rates are still on the rise. Dayton, Ohio, and Tempe, Arizona, both experienced increases over 5 percent since April for one-bedroom units. Houston and New Haven, Conn., both experienced jumps in rent for two-bedrooms as well.

Philadelphia's rent swing made national lists only for one-bedroom units. Rental rates for two-bedroom apartments here remained flat since last month at $1,499.