Accents are sometimes quite marked; notable accents are found in speakers from Phhom Penh (the capital city) and Battambong.
(This analysis comes from my observation as a conversant speaker of Cambodian without any background in linguistics).
A notable characteristic of the Phnom Penh accent is a tendency toward slang and laziness in pronunciation, much like American urban slang. For instance, "Phnom Penh" will sometimes be shortened to "m'Penh". Another characteristic of the Phnom Penh accent is observed in words with an "r" subconsonant in the first syllable (that is, where r is the second consonant, as in the Enlish word "bread"). The r is not pronounced, the first consonant is pronounced harder than usual, and the syllable is spoken with a dipping tone much like the "hoi" tone in the VietnameseLanguage. For example, I have heard the word "dre" (meaning "fish") pronounced "te"; the "d" becomes a "t", and the vowel (long A) begins low and rises in tone.
[This seems like a schwa - an unstressed neutral sound, like in "poor" right before the r or at the beginning of "about". Sometimes English r's get weakened to schwas. Same deal here? No, not as far as I can tell. The r is rolled normally, and completely omitted in the manifestations of the Phnom Penh accents Ive heard.]
Cambodian written language is alphabetic like English (and unlike Chinese). Its alphabet consists is written in two separate parts--consonants and vowels. Pronunciation is given here in the traditional form (you will need to have a computer with Khmer fonts to see the letters below).
ក gaw ខ kaw គ go ឃ ko ង ngo ច jaw ឆ chaw ជ jo ឈ cho ញ nyo ដ daw ឋ taw ឌ do ឍ to ណ naw ត Daw ថ taw ទ Do ធ to ន no ប ? ផ ? ព ? ភ ? ម ? យ yo រ ro ល lo វ vo ឝ saw ឞ ? ស ? ហ haw ឡ law អ aw