Try this page:
http://manybooks.net/categories/PUL
All the books are either public domain or creative commons, in other words, free. I'm not sure what Turkey's copyright laws are.
BEWARE manybooks do now carry some books which are priced, just avoid these if you want.
Also, if you find a book you like, check to see if it's in the MobileRead library - the books here are better formatted than they are at manybooks.
Have fun!