You don't have to be a dairy farmer to like a cash cow. Stocks of companies that generate lots of free cash flow year in and year out are the investing equivalent of the prized cow that provides plenty of milk for a long period of time.

Some stocks that are cash cows, however, come with steep valuations. Why buy the cow if the milk is expensive? You don't have to. There are some cash cows generating loads of free cash flow that have reasonable valuations. Berkshire Hathaway (NYSE:BRK-A) (NYSE:BRK-B), Gilead Sciences (NASDAQ:GILD), and Pfizer (NYSE:PFE) are high on the list of top stocks that are cash cows. And they're attractively priced right now.

Figure of cow made up of dollar symbols

Image source: Getty Images.

Berkshire Hathaway

Warren Buffett loves companies that spin off lots of cash. Therefore, it's not surprising that his own Berkshire Hathaway ranks as one of the best on the market in generating free cash flow. Over the past 12 months, Berkshire has created free cash flow of $33 billion. That's a big jump over the company's historical free cash flow levels, primarily because of a positive impact from loss adjustments. Still, though, Berkshire Hathaway has a solid track record in spinning off cash. 

The stock is relatively inexpensive for the amount of cash flow it generates. Berkshire shares trade at less than 15 times free cash flow. That makes the stock look more attractively valued than does its forward earnings multiple of more than 24.

Of course, the important thing over the long run is how Berkshire Hathaway will use its enormous free cash flow. Warren Buffett and others he has brought into the company have invested Berkshire's cash very well in the past. Buffett pointed out in his letter to shareholders earlier this year that the stock generated compounded annual gains of 20.8% from 1965 through 2016. Berkshire has done even better this year, with a year-to-date gain of nearly 22%.

Not every investment made by Buffett and Berkshire turn out to be a winner. However, enough of them do that the stock keeps on rising -- and Berkshire keeps on generating more free cash flow to pour back into further investments. That's a great recipe for long-term success.

Gilead Sciences

Gilead Sciences produced free cash flow of $11.8 billion over the past 12 months. Investors can buy that cash flow on the cheap: The biotech stock trades at roughly 8.5 times free cash flow.

There's a catch for Gilead, though. It's free cash flow is falling, as are its revenue and earnings, as a result of challenges for the company's hepatitis C virus (HCV) franchise. Gilead faces competition in the HCV market, but the bigger issue is that the new generation of HCV drugs have cured so many patients that there aren't as many remaining to receive treatment.

However, I think Gilead stock is a smart long-term pick. While its free cash flow is slipping, Gilead still is generating more cash flow than it did before 2015. And there could be an end in sight to the bleeding. Gilead CEO John Milligan recently stated that he expects the rough waters in the HCV market will become smoother, with 2018 potentially bringing the "beginning of a growth phase" for the company.

I also like how Gilead will probably use its free cash flow. The company pays a nice dividend, which currently yields 2.74%. More important, Gilead is using its money to make acquisitions that should fuel long-term growth. The biotech completed its acquisition of Kite Pharma in October and just announced a buyout of Cell Design Labs. I expect more acquisitions will come that add to Gilead's product lineup and pipeline.

Pfizer

Another big drugmaker is also a major cash cow. Pfizer generated free cash flow of $14.3 billion over the last 12 months. The pharma stock trades at a little over 15 times free cash flow, which isn't bad at all. 

Like Gilead, Pfizer has put its cash flow to good use. The company pays one of the best dividends in healthcare, with a current yield of 3.53%. Pfizer has also bought back a lot of its shares, spending $5 billion in the first nine months of 2017 on stock repurchases. 

While Pfizer made a couple of key acquisitions in 2016, the drugmaker hasn't made any significant deals this year. However, some industry observers think Pfizer could be looking for a really big merger or acquisition in the not-too-distant future, especially with the increased likelihood that corporate tax reform will be implemented in the U.S.

It's probable that Pfizer will be an even bigger cash cow in 2018. The company's earnings are expected to be higher than they've been in recent years, with fast-growing products like cancer drug Ibrance and blood thinner Eliquis. And it could have more cash on its hands from another move: Pfizer is considering selling or spinning off its consumer healthcare business.   

The moo-ral of the story

As we've seen from these three companies, it's not the free cash flow itself that's important for investors. Instead, it's how businesses use the free cash flow that they generate. You'd be better off paying a higher price for a company that uses its free cash flow wisely than a lower price for one that doesn't.

Berkshire Hathaway clearly performed really well over the years in using its cash flow. Gilead Sciences has used its cash flow to invest in a few acquisitions that didn't pay off, but the biotech has been pretty effective overall. Pfizer probably has the spottiest record. Many think the company has paid too much on some of the deals that it's done in the past. However, Pfizer has beaten the S&P 500 in total return over the last 10 years, which shows that it's done a pretty good job at using its cash flow.

If you're looking for cash cows that aren't too expensive and that should provide plenty of cash flow for years to come, I think Berkshire Hathaway, Gilead Sciences, and Pfizer are good ones to put in your barn. 

Keith Speights owns shares of Gilead Sciences and Pfizer. The Motley Fool owns shares of and recommends Berkshire Hathaway (B shares) and Gilead Sciences. The Motley Fool has a disclosure policy.