Warren Buffett is known for buying "great businesses at fair prices." As of this writing, Berkshire Hathaway's (NYSE:BRK-A) (NYSE:BRK-B) portfolio features the common stocks of about 45 companies, which consist of some of the most well-respected and consistent long-term winners in the market.

However, because of changes in market conditions over time, some of Buffett's stocks appear to be better values than others right now. Here are three stocks from Buffett's portfolio that could let you do what Buffett himself loves to do -- buy great companies at an even better price.

1. A few minor and temporary issues, but still the best at what it does
American Express
(NYSE:AXP) shares have fallen by about 12% so far in 2015, thanks to a few major issues.

AXP Chart

For starters, Costco (NASDAQ: COST) dropped American Express as its exclusive credit card partner. And while this may not sound too significant, consider that 10% of all American Express cards are Costco co-brand cards, and 8% of AmEx's credit card spending is from Costco cards. So this will indeed hurt AmEx in the short term, but the company should be able to make up for the lost business elsewhere over time.

Also, American Express just lost a significant legal battle. As a result, AmEx is no longer allowed to prohibit retailers from encouraging customers to use other cards, such as Visa or MasterCard. Since American Express cards are the most expensive type for retailers to accept, there is a motivation for retailers to offer discounts or perks to consumers who choose to use lower-cost products.

However, American Express is still a long-term winner. The company is the undisputed leader at creating exclusive "clubs" of cardholders and attracting affluent customers who are desirable to retailers, and this is precisely why the company can get away with charging retailers more than its competitors and will continue to be able to do so. These developments are just minor setbacks (many investors and analysts expected the legal ruling), so the recent price drop is simply an opportunity to get into an excellent company at a more attractive price.

2. International headwinds create an opportunity
Procter & Gamble
(NYSE:PG) is a stock that fell recently because its earnings report disappointed investors.

PG Chart

Specifically, because Procter & Gamble conducts a significant portion of its business overseas, it's vulnerable to currency fluctuations, which are exactly what hurt the company's latest quarterly earnings. The stronger U.S. dollar and the weakness in several other currencies, such as the Russian ruble, caused P&G's quarterly earnings to fall by about 9% compared to the year-ago period. It also forced the company to reduce its guidance for 2015; a 12% year-over-year drop in profit is now expected.

However, these issues should be temporary. Procter & Gamble has a remarkable portfolio of household-name brands such as Tide, Pampers, Gillette, and Charmin, just to name a few, and it remains one of the most rock-solid companies in the world. These are brands that consumers recognize and use all over the world, and they will continue to be for decades to come.

Plus, Procter & Gamble is in the elite rungs of the dividend aristocrats, with 58 years of consecutive dividend increases, and there is no reason to believe that streak will end anytime soon.

3. Oil's weakness means bargains for those with patience
The plunge in crude oil prices has affected the portfolios of millions of investors, and Warren Buffett is no exception. Berkshire has a significant stake in National Oilwell Varco (NYSE:NOV) that has fallen by more than 35% since last September. And while nobody can predict when oil will bottom out, or when it will recover, National Oilwell Varco is an excellent choice for investors with the patience to wait and see.

NOV Chart

The main reason I like National Oilwell Varco is that it has a "wide moat," as Buffett would say, meaning that it has such a broad reach that it's relatively safe from its competition. Specifically, the company estimates that 90% of offshore rigs and the majority of the world's larger land-based rigs use components that National Oilwell Varco manufactured. That's a pretty broad customer base.

No "bad" choices in Buffett's portfolio
While I believe these three stocks represent excellent buying opportunities right now, there are few stocks, if any, in Berkshire's portfolio that I'd refer to as "bad" investment choices.

Having said that, if you don't want to stock-pick, then there is nothing wrong with simply buying shares of Berkshire. Doing so will get you exposure to all of the stocks the company holds, as well as Berkshire's fully owned businesses, such as Geico and NetJets.

However, some stocks always look more attractive than others at any given time, and these three could be the best buys in Berkshire's portfolio full of very attractive stocks.