Wat Mahathat, in Ayutthaya, is a temple that was quite thoroughly ransacked by the Burmese. Several leaning prangs of Ayutthaya are still feebly defying gravity though, and the rows of headless Buddhas are atmospheric.
This is also where you can spot the famous tree that has grown around a Buddha head. When taking pictures of you and the Buddha head, make sure you kneel to show respect, as it is considered holy by Thais.
Price: 50 baht