There are so many Khmer fonts out there these days. This might be a very hard decision which one you should use. Each type of fonts has its own advantages and disadvantages. The Khek Brothers work very well for across plaforms (free download PC & Mac) when file is saved in Plain Text, but they cannot be typed without purchasing KHEK keyboard. However, there is no body knows if Khek Brothers going to update their keyboard to work with later version of OS such as Windows 7 or Mac OS (higher than OSX). The earlier Khmer fonts (free download) can be typed using United International keyboard. These two vendors fonts have the same size and weight of English Arial and work well in most applications Adobe products and QuarkXpress except for html. I have been using these two types a lot but lately mainly use the Khek Brothers for easier switching platforms.
The Khmer Unicode might be the future of Khmer language and they are free but do not work well in many applications, such Adobe products and QuarkXpress. They also crushing too much in Microsoft word. However, they work better in html if within application such as Microsoft Expression Web. The Limon fonts are commonly used in Cambodia because they are free, using United International keyboard and work in most applications. However, they are not the same size as English Arial. Thus, it would take more time for switching between Khmer and English characters. Please note that each type of font vendor cannot be switched because each one of them using different key stroke to produce Khmer character. Only most of the main characters are compatible but not the subscript (legs), superscrip (hair) or wovels.
Khmer Fonts Resources