Don't invest in plain gold coins. Buy "rare" gold coins. Especially the rare Saint-Gaudens Standing Liberty $20.00 gold pieces. Try to find some with a high relief and that have been graded by the ANA, with at least MS62 or better. If they haven't been graded by ANA, then make sure you have them graded. You will not only have the bullion value, but, also the collectability to consider in it's overall value.
