This presentation is mainly based on an article in Flag Bulletin [tfb] (No. 133, p. 3-15; title: "New flags - State of Cambodia"; author: presumably Whitney Smith [smi90]). Further sources: Flaggenbuch [neu39], Die Zeichen der Menschen und Völker: Unsere Welt in Fahnen und Flaggen and Lexikon Flaggen und Wappen [smi75d]. Especially difficult are, of course, the political circumstances leading to the fact, that at certain times (at least) three flags of different governments and counter-governments had been used to represent Cambodia.
Flag during French Protecdtorate, 1863-1948
ca. 1863-1948 (Kingdom of Cambodia under French protection): The first Cambodian flag probably came into existence around 1863 and was used, with only variations, until 1948. It was a red field with a blue border and a white representation of Angkor Wat in the center. The image is based on the image in Flaggenbuch; a different variant is shown in the Flag Bulletin article: the Angkor Wat is drawn like in the current flag.
Kingdom of Cambodia, 1948-1970
On 20 October 1948 a new flag was adopted, namely a horizontal triband (1+2+1) of red, blue and red with the Angkor Wat in white in the centre. The Angkor Wat is usually shown outlined in red (Flags Through the Ages and Across the World). This is basically the flag in use again now This flag was used until Norodom Sihanouk was overthrown in 1970. However, it was used after that in exile and in parts of the country under the control of Sihanouk troops. According to the Flag Bulletin article it also appeared for a short time again at the UN headquarters from about April 1975 to January 1976. It was reestablished in Cambodia itself 30 June 1993.
1958 Chief of Naval Staff
Khmer Republic, 1970-1975
Lon Nol overthrew Sihanouk in 1970 and on 9 October 1970 a new flag was introduced. It showed a blue field with a red canton; in the canton a white representation of Angkor Wat (three towers), in the upper fly corner three white stars. This flag was used until April 1975. Obviously this had not been used afterwards in exile or by anti-government forces.
In April 1975 the Khmer Rouge forces had established control of most of Cambodia, including the capital Phnom Penh. For a while Norodom Sihanouk acted as a puppet head-of-state of the "Democratic Kampuchea". At least at the UN the 1948-1970 flag was reestablished until January 1976. Inside the country plain red flags seem to have been used (according to Flag Bulletin article).
Democratic Kampuchea, 1975-1979
In January 1976 the new constitution of "Democratic Kampuchea" established a new flag. It was a red field with a three-towered yellow representation of Angkor Wat; however, this was much stylized and only called "monument", not "Angkor Wat" in the constitution. This flag was used until January 1979, when the Khmer Rouge government was deposed. However, it continued to be in use in the parts of the country, where Khmer Rouge forces waved a guerilla war against the government. Furthermore, as the "Democratic Kampuchea" government was the internationally recognized government, it was also used abroad, e.g. at UN headquarters, until 1991. It is unclear to me, however, when this flag had been used for the first time. It was definitely not a new invention in 1976, but had been used previously by the Khmer Rouge. It was used in Germany during demonstrations against the war in Vietnam and Cambodia (17 March 1973 and 29 April 1973). The demonstrators were members of the Maoist KPD, that also displayed Pathet Lao and Vietcong flags (Rote Fahne Vol. 4, iss. 12, p. 1 and vol. 4, iss. 18, p. 3).
People's Republic of Kampuchea, 1979-1989
In December 1978 a Khmer Rouge dissident faction (under Heng Samrin and Hun Sen) invaded Cambodia together with Vietnamese troops, and deposed the Khmer Rouge government in Phnom Penh in January 1979. The new People's Republic of Kampuchea introduced a flag based on the 1976-1979 flag, but having five towers instead of three. This flag was used until 1989 in the country, but was not recognized internationally (e.g. at the UN).
State of Cambodia, 1989-1991
On 1 May 1989 a new flag was introduced, together with an alteration of the name to "State of Cambodia" and a new constitution. The new flag was a bicolour of red over blue, showing a yellow representation of Angkor Wat (five towers) in the centre; the flag Bulletin article and [heh90] show the Angkor Wat very detailed (similar to the 1948-1970 flag) and not stylized as in the 1979-1989 flag. The stylized version might have been in existence, though.
1991-1993 (UN administration)
Under the UN administration (UNTAC = United Nations Transitional Authority in Cambodia) Cambodia used a UN blue flag with a white map of the country in the centre (and the blue inscription of the country's name). However, I'm not sure when this flag was introduced. The claim that it was from 24 June 1991 seems a bit early to me. The most important steps to peace in Cambodia happened only in October 1991 (peace treaty in Paris; decision of UN security council to send UN peace forces).
Kingdom of Cambodia, 1993-Present
