Off the island
Wat Chaiwatthanaram
Due to flood damage, this temple is currently closed. However you can still walk around the outside for free and take pictures. The temple that graces the official tourist pamphlet for Ayutthaya, this Wat is a must see. Many intact pagodas surround a central chedi that you can climb from all sides. A nice view of the city can be had from the top. Very photogenic.
Wat Na Phra Mane
This Wat offers a mix of old and modern buildings. It is unique because it survived the destruction of the city in the 18th century. Of interest are the vaulted ceilings and a Buddha made of black stone
Wat Phanan Choeng
A working monastery located south of Ayutthaya, no one knows how old it is, but it existed before Ayutthaya was founded as the capital. It contains the oldest large cast bronze Buddha image in Ayutthaya, called "Phrachao Phananchoeng", built in A.D. 1325; it is made of stucco in the attitude of subduing evil. A small room to the right of the main hall contains a nice collection of Buddha images and the room is painted with many individual unique pictures, in bright colours offset with gold.
Much of Ayutthaya's history revolves around trade with other nations, but these nations were not allowed to set up camp inside the city walls. Thus, surrounding Ayutthaya's waters are plenty of remains from the countries that once set sail here, such as the settlements of Japan, the Netherlands and Portugal, as well as the interesting Thai-Chinese temple of Wat Phanan Choeng.
On the island
Wat Phra Ram
This temple consists of one huge prang and some smaller Chedi and outbuildings, all in disrepair though the top of the prang is complete. Staircases to the side of the prang give views of Ayutthaya. This monastery was located outside the grand palace compound to the east. King Ramesuan commanded it built on ground where the royal cremation ceremony for his father, King U-Thong, took place. A big lagoon is in front of this monastery. Its original name was "Nong Sano"; it was changed to "Bueng Phraram" and currently is Phraram Public Park.
The temples with entry charges are usually in ruins, so there is no dress code, although visitors are still requested to refrain from blatant stupidity like clambering up the Buddha statues. Working temples tend to charge no fees and there are often no officials to check that a dress is appropriate though it is advised to follow these customs to show respect for sacred places.
Viharn Phra Mongkol Bopit
An impressive building that houses a large bronze cast Buddha image. It was originally enshrined outside the Grand Palace to the east, but it was later transferred to the current location and covered with a Mondop. During the second fall of Ayutthaya, the building and the image were badly destroyed by fire. The building currently seen was renovated but does not have as beautiful craftsmanship as the previous ones. The open area east of the Sanctuary Wihan was formerly Sanam Luang, where the royal cremation ceremony took place.
Ayutthaya is 76 kilometres north of Bangkok and boasts numerous magnificent ruins. The ruins indicate that Ayutthaya was one of Southeast Asia's and probably the world's most prosperous cities in the 17th Century and beyond. Phra Nakhon Si Ayutthaya Historical Park, a vast stretch of historical site in the heart of Ayutthaya city, has been a UNESCO World Heritage Site since December 13, 1991.
There were three palaces in Ayutthaya: Grand Palace, Chantharakasem Palace the Front Palace and Wang Lang the Rear Palace. In addition, there were many other palaces and buildings for royal visits located outside Ayutthaya, such as the palace at Bang Pa-In and Nakhon Luang Building at Nakhon Luang.
It seems there is a scam, but not against tourist but against government. Ladies selling tickets take the money from you and allow you to enter, but will not give you a paper ticket and probably take the money to their own pocket. If you want your money to go for temple renovation and conservation instead of going into private pockets, insist a paper ticket.