Here is some information on Galaxy S3 ROMs.
AOKP
AOKP for AT&T Galaxy S3 [Guide]
Ice Cream Sandwich
kyan's Blog [ROM][I747MVLALH1][09.12.12]kyanROM 1.5 READY
JellyBean
[ROM][JB]BlackJelly V 1.01 LK3 - 12/06/12
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