The official currency of Turkey is the Lira. Therefore, the Turkish Lira is the currency to take on a trip to Turkey.
If you live in the United States, the flight to Turkey likely has a stopover in a western European nation such as Germany, France or England. All three of these nations and the majority of western Europe use the Euro as their official currency, so it is wise to bring along some Euros to pay for dinner at the airport or a hotel stay during your layover. Bringing cash instead of using your credit card can help avoid the foreign-transaction fees that many credit card issuers charge.