These two Buffett stocks are too good to pass up for patient, long-term investors.Want to help your portfolio? Watch what Warren Buffett is buying. His stock picks have, on average, crushed the market over the long term. And right now, two of his top holdings look too good to pass up.This is a company you can buy and hold foreverGreat companies can figure out how to generate impressive returns for shareholders without resorting to taking on excess debt. For decades, American Express (AXP -0.18%) has done a ...