I imagine a good way to learn is to find substantial forks from either the bitcoin source (https://github.com/bitcoin/bitcoin) or litecoin source (https://github.com/litecoin-project/litecoin).

This is something I am interested in as well. At the very least, I'd like to look at the full commit history of a coin that was forked from another coin (which is, basically, every coin aside from bitcoin). A number of alt coins don't contain this history, but I am sure some of them do. Anyone have an example of the full fork commit history of an alt coin?