As other posters have mentioned, it's hard to find cabs that happily and willingly take credit cards. If you're insistent on paying with plastic, your best bet is to call a cab dispatcher and request a cab who will take a credit card. If you're really convinced that you'll lose $20 bills right and left, then I'd recommend withdrawing small amounts of money from an ATM immediately before hailing a cab. (No offense, but "losing cash" sounds like a lame excuse. Should I be following you around because you're likely to be leaving a trail of cash, keys, iPods and credit cards in your wake?) Or, buy a CTA pass and plan on taking the bus & El.