Angkor Wat is the largest sites in the region.
Do not miss the sunrise. It will get up early and push you into the night to a quiet corner, but then the moment is magic, install and let yourself be soothed by the music ... distant.
The other advantage to go early is to visit the temples without having to bear the mass of tourists who arrive 2 hours later.
Do not hesitate to hire a local guy to serve as a guide, they will take you to places you fabulous while telling the history of places with less stringent than the guides. In the neighborhood there are dozens of other temples to visit, Bakeng, Bayon, Phreakan, Takeo, Thon ...