See the main temples on the first day along with the floating village on the Tonle Sap. On the second day, go to see some temples a little away from Siem Reap.
Day 1 - Angkor Wat, Angkor Thom, Bayon, Ta Prohm, and Floating Village
Day 2 - Banteay Srey, Beng Mealea, and Roluos Group (Preah Ko, Lolei, and Bakong)