Hey! At first, Su-37 was built in one number and it has been crashed in 19 December 2002(pilot is ok)
So Su-37 is a modified Su-35 (it's not the same to new Su-35S) by installing thrust vectoring, and Su-35 is a modified Su-27M =)

We have a russian site with info and photos there, but it's on russian http://www.airwar.ru/enc/fighter/su37.html