If the credit card is fron a bank, you can drop it off at one their branches and they'll contact the owner. Or if there's ID, you can take it to the address's nearest police precinct and have the police return it, if you don't want to show up to some stranger's home to do it yourself. I've done both for a card I found on 6th Ave and an ID I found by the 34th street Macy's.