i think nas, jay, and x have all had unofficial GHs out; i'm waiting for official ones. D12 needs to put out 1 or 2 more cds.
i think GHs of course need to have all the singles, and also some cult favorites or underground hits. i also think that ones that include new verses or drastically changed lyrics need to be included rather than the album versions (such as "Just a moment" or "One mic", the latter which i like better than the album version). also, to get people who already have all the songs to buy it, put a few new/unreleased tracks on there, such as soundtrack, compilation, or guests appearances.
one that i think NEEDS to be included on DMX's is the dirty version of "slippin".