CyanogenMod 10, the custom build of Android based on 4.1 Jelly Bean, has just made its first showing. The team has released a preview build of CM10 on the Samsung Galaxy S III for AT&T and T-Mobile, and another developer has done the same for Sprint's S III. It's only been a couple of weeks since CM10 was even announced, so this is a very rough first version, to be installed at one's own risk. It's also, however, the first step towards putting a clean, highly-regarded custom Android version on one of our top smartphone picks. Unfortunately, the locked bootloader makes it less likely we'll see similar work put in for the Verizon version.
Samsung has been one of the more CyanogenMod-friendly developers, and it notably hired CM founder Steve Kondik last year. Even if you don't end up installing CM10, the S III's TouchWiz interface is still free of the bloat that often drives people to CyanogenMod.