From an ecological perspective, Tonle Sap is incredible, and it has entire floating villages on it. We took the fast boat from Siem Reap to Phnom Penh over the Tonle Sap - mainly because I wanted to see it. I'll post photos later.
Bantay Srei is the "women's temple" because the carvings are so beautiful they must have been made by women. I will post photos later. This and Ta Prom may have been my favorite temples.