Oh he who chose to commemorate the Obiedient One

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I am by no means an expert, but I'll give your question a shot.
First, there are several "Eastern Churches" and each Church has its own traditions. The most visible one in the US is actually a European church, the Byzantine Church.
For the Byzantine Church, the first musical website that comes to my mind is the Greek Orthodox Diocese of America's website, in the music section
here [
goarch.org] .
I'm told that it's not 100% authentic "Byzantine Chant" (much in the same way Gregorian chant with an organ, which we heard at the Papal Masses, isn't 100% authentic Gregorian Chant), but it's a reasonably good starting point. Chant CDs are also available online if you want to search further.
Also note that within the Byzantine Church there are several traditions of chant. Thus, different traditions will have different music. The Ukranians, Carpatho-Rusyns, and Muscovite Russians each have their own style of music. This is similar to how the Roman Church has Gregorian Chant, Old Roman Chant, Mozarabic Chant, Ambrosian Chant, Sarum Chant, Sacred Polyphony, among others.
Marc
[edited to change the initial address to reflect the comment below

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