I usually run 35 psi even if the sticker says different on regular passenger tires. The ride will be a little more harsh but the gas mileage should get better. Max pressure of a passenger tire is usually 35.
If you have any type of high performance tire, look on the tire for the max psi. They are usually higher. In my Stratus R/T with 18'' wheels the max psi is 44 and I keep them at 40. The 20's on my Durango have a max psi of 50 and I keep them at around 42-43psi.