Turkish government: http://www.mfa.gov.tr/visa-information-for-foreigners.en.mfa

Turkish consulate US: http://istanbul.usconsulate.gov/tourist_visa.html

Turkish consulate London: http://www.turkishconsulate.org.uk/en/visa.asp?PageID=2

Turkish consulate in The Netherlands: http://rotterdam.cg.mfa.gov.tr/