One of the issues with the current Khmer Unicode fonts is the English characters included do not look good (and this is understandable as they were not meant to be used as English fonts).  But for some, we use both English and Khmer, especially when it comes to a system user interface (like OpenOffice).  We recently combined the KhmerOS System font with Liberation Sans to create an appealing system font for both English and Khmer.  For instructions on how to use this font as your system font in OpenOffice please click here.