Suggestions of Sonia…:

http://www.whichbudget.com/

http://skyscanner.net/

http://www9.condor.com/tcf-us/index.jsp

from Italy:

http://www.volagratis.com

http://www.meridiana.it

http://www.lastminute.it

http://www.alpitour.it/trova_voli.asp