Visa requirements

It is always a good idea before visiting Turkey, you to check the E-Consulate website to determine if you need a visa. The website also provides details of required fees.

Citizens of the following countries can get a sticker-type entry visa at the point of entry into Turkey for a fee:

Valid for three months:

UK (cost: US$20 / €15 / £10)
US (cost: US$20)
Canada (cost: €45) Apparently Canadians get shafted on the Visa cost because our government is encouraging Turkey to recognize the Armenian genocide, which Turkey denies ever happened.
Australia (cost: $20 / €15)
Ireland (cost: €10)
The Netherlands (cost: €10)
Italy (cost: €10)
Portugal (cost: €10)

Valid for two months:

Ukraine (cost: US$20)

Valid for one month:

Slovakia (cost: €10 or US$15)
Azerbaijan, Moldova, Russia (cost: EUR10 or US$15)
Serbia (cost: €10)

German citizen don't need a visa for stays up to 90 days and can even enter with their national ID card (Personalausweis) or an expired passport/ID unless arriving at the non-Council of Europe land border crossings (i.e. from Iran, Iraq and Syria).

For more information please visit Turkish Culture and Tourism Office website.

Source: (Wikitravel)