Capital One Financial ( COF -3.23%) is one of Berkshire's smaller bank stock holdings, with a stake of 2.6% of the bank worth "only" $1.6 billion. But for long-term investors, Capital One looks like a tremendous value and has some interesting growth opportunities in the future.

Although Buffett didn't retain his original shares, he later made American Express a significant holding for Berkshire Hathaway beginning in the early 1990s. Today, Berkshire Hathaway owns a substantial 21.3% stake in American Express, making it the holding company's second-largest stock position, surpassed only by Apple.

Berkshire Hathaway sold Bank of America stock in nine straight trading sessions to close the month of August and into the start of September, resuming a sell-off that started in July when the bank's stock hit a two-year high.