Turkish currency is the lira, abbreviated as TL. There are coins of 50,000 (written on the coin as "50 bin") and 100,000, and notes of 250,000, 500,000, 1,000,000, 5,000,000 and 10,000,000. Bear in mind that the 5,000,000 note looks very similar to the old 100,000 one, and it's not unknown for visitors to be fooled into accepting the worthless lower denomination. Rates for foreign currency are always better inside Turkey, and because of the TL's constant devaluation you should change money only as you need it. Many pensions and hotels, particularly in the popular destinations, will quote prices in US dollars as well as TL and you can pay in both.
Banks are open mainly Mon-Fri 8.30am-noon & 1.30-5pm, although some, notably Garanti Bankasi, open at lunchtimes and on Saturdays. Most charge a commission of about US$2.50 for travellers' cheques. Between April and October many coastal resorts between Çanakkale and Alanya have weekend and evening hours at specific nöbetçi banks; a list is posted in the window or door of each branch. You can also use the exchange booths run by banks in coastal resorts, airports and ferry docks, though some charge a small commission. Easiest option is a private exchange office, which will offer competitive rates and charge no commission. Almost all bank branches have ATMs which accept Cirrus and Plus, but it's wise to use them during banking hours in case your card is swallowed; avoid stand-alone ATMs for the same reason. Post offices in sizeable towns also sometimes change currency and travellers' cheques, for a one-percent commission.