Although these examples are for TOEFL independent essay, they are well structured and helpful to learn how to write an essay.

http://www.goodlucktoefl.com/free-sample-toefl-essays.html
http://jasonrenshaw.typepad.com/ibt_speaking_writing/ibt_writing_qu_2_independent/
http://www.testmagic.com/Knowledge_Base/Toefl/Writing/samples/index.htm