An attempt at an exhaustive list of downloadable Unicode and non-Unicode Khmer fonts is hosted at  selapa.net.

Khmer font resources are also available at  cambodia.org.

30 Khmer fonts are listed at  wazu.jp. Not all of these are downloadable from the site.

The  Khmer Software Initiative contains fonts which can be used to write both the Latin and Khmer alphabets without changing text size.