According to my personal test in between various travel sites, the followings are the best travel sites which offer the cheapest flight tickets to Turkey.

– it is hard to come across a cheaper European flight other than SkyScanner

Skyscanner is a search engine technology company based in Edinburgh with a big ambition to become the number one online resource for travel information.

– the lowest international airfares on the web

Economy Travel is one of the oldest ticket search engine of the web. They are in the business since 1988 and so far the most popular “cheapest airfare source” for the budget travelers.

– offers the cheapest flights worldwide

Kayak is a travel search engine, searching hundreds of travel sites from all over the world to bring you the cheapest fares it can find. The results are nicely sorted by price, and once the search is complete, you can tweak and filter the results to find the perfect ticket for your needs. Once you make your choice, it sends you to the travel sites to make your purchase. Because Kayak searches all travel agents from all around the world, it almost provides the best prices all the time no matter where you are flying to.