Here's a list of fonts I know about but didn't manage to get the hand on... If you have them, please send them to me!

Souriya Chrieng Souriya Chrieng by Zachary Quinn Scheuren. You can also read his essay about the history of khmer printing types.
Mirna Khmer Mirna Khmer by Teja Smrekar
Roaat Regular Roaat Regular by Jasper Habicht, author as well of Sievphou Seksaa.
Monotype Khmer Monotype Khmer was part of their WorldType system. It seems to be still available as part of their Andale and WorldType Collections but it doesn't look really useable.
Robam Khmer MT Regular Robam Khmer MT Regular by Monotype.
Vat Kdol François Bizot created his own font for his publications. The text font is called "Vat Kdol", no idea about the title one...
Jehovah’s Witnesses The Jehovah’s Witnesses use their own set of fonts in their publications.
LaserCambodian LaserCambodian by Linguist's Software provides the CambodianLS and CambodianLSU font families.
Frédéric Snauwaert While working for a Singapore based design company, Frédéric Snauwaert developed a Khmer typeface for big-scale use.
Krochma Krochma by Visay Seng.
CDT CDT (Cambodian Digital Technology) had some of the first unicode khmer fonts: CDT Mool Angkor, CDT Text Kampuchea, CDT Text Mondulkiri, CDT Text Bavet and Camboday, all by Om Mony.
CyberCambodia CyberCambodia used to sell some fonts: Samrae (and variants), Rum Peun and Phnom Kraom.
Morn Mon Besides the 3 ones he had published on his website, it seems Morn Mon has made more of them.
athch5 YouTube user athch5 used a handwritten font in many of his videos.
École Khmère de Courbevoie Khmer Courier, Khmer Chaktomukh, Khmer kbachmoule, Khmer kbachmoule Reussey, Khmer Reussey and Khmer OCR-A were in use at the École Khmère de Courbevoie in the ’90s.