a basic way to do it would be to just download an existing ROM (say, MCR's one) and extract the file. Delete/add the apps you want and make sure the update script and build.prop will still work. Once you're done, zip it, sign it and flash it. It's pretty easy.
...however, I would like to know how to build Android from the AOSP source for a plain vanilla distro. Some of the Samsung additions really get on my nerves, and I'm positive that a vanilla Froyo (or even Eclair) build would run rings around the stock SGS.
Samsung Galaxy S III
Transformer Pad TF300T
::: Old devices :::
Samsung Galaxy S
LG Optimus 2X
Asus EeePad Transformer TF101
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