Wiktionary:Frequency lists | khmer
The online dictionary http://kheng.info has by far the best frequency list. It also has a box where you can paste items from the list and it hyperlinks the words to immediate recorded pronunciation. Just copy and paste from the "Frequencies" page to the "Read" page. It actually contains pronunciations for almost all of the first 1000, and most of the first 2000. The entire frequency list can be downloaded at the bottom of the "Frequencies page". The anonymous creators of the site have done an enormous job to advance Khmer learning.