The stock market has boomed this year, but as stock prices climb and valuations get stretched, high dividend yields are getting harder and harder to find. The S&P 500 offers a dividend yield of just 1.8%, and income-seeking investors can't really turn to bonds, as treasury rates are near historic lows.

Luckily, there are still some solid dividend stocks available that income investors can take advantage of. Keep reading to see why these Motley Fool investors recommend Rio Tinto (NYSE:RIO)GlaxoSmithKline (NYSE:GSK), and 8point3 Energy Partners (NASDAQ:CAFD)

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This metals stock is so hot, it could be molten

Rich Smith (Rio Tinto plc): Mining stocks have been so bad for so long that it may take investors a while to notice once things start getting less bad. At British metals megaminer Rio Tinto, that's already starting to happen.

With products ranging from aluminum to iron to titanium dioxide, diamonds, gold, and... salt, Rio Tinto's operations span the globe, ranging from Asia to America to Europe, and even Australia. What's more, after three straight years of declining sales, things are starting to look up for Rio Tinto again as global demand for iron ore rebounds and Rio responds with an expansion of its Silvergrass mining project.

Sales in the first half of 2017 grew 25% in comparison to year-before levels, and profits nearly doubled to $3.3 billion. Annualize that out and Rio Tinto appears to be on course for $6.6 billion in profits this year (which would value this $88 billion stock at just 13.3 times earnings -- a near-50% discount to the average P/E ratio on the S&P 500). Cash profits are even richer at Rio (and the price-to-FCF ratio accordingly lower), with free cash flow exceeding $4.5 billion in this year's first six months. This gives Rio Tinto a lot of cash to shower upon its shareholders in the form of a 4.9% dividend -- a dividend that's rising along with income yet still consumes only 49% of profits.

Between the generous dividend and an earnings growth rate that analysts estimate at 11.7% over the next five years, I consider Rio Tinto a top stock for dividend investors today.

A monster yield in pharma

George Budwell (GlaxoSmithKline plc): GlaxoSmithKline presently sports a dividend yield of a jaw-dropping 5.71%. To put this figure into the proper context, Glaxo's yield is roughly double the average of its big pharma peer group. 

Why? Glaxo's stock has been sinking for over a decade now because of its inability to move beyond the long-lived asthma medicine Advair as its flagship product. Despite its falling share price, however, the drugmaker's management team has stubbornly resisted slashing the dividend. 

Glaxo's monstrous yield might not be a key reason to buy its stock for all that much longer, however. Although Glaxo's new CEO, Emma Walmsley, has stated that the dividend will remain at current levels until at least 2019, the company has been sniffing around Pfizer's consumer healthcare business in recent quarters. This acquisition, if it happens, could add a sizable amount of debt to Glaxo's already stressed-out balance sheet, triggering a shift in capital allocation.

At the end of the last quarter, after all, Glaxo's debt-to-equity ratio stood at a worrisome 394.16. So taking on even more debt probably wouldn't be welcomed by Wall Street, especially if it sparks a dividend reduction. And if the company's unsightly debt-to-equity ratio wasn't enough of a concern, Glaxo's trailing-12-month payout ratio of 169.8% is arguably reason enough for income investors to run for the hills.

Putting all this doom and gloom aside, however, there are some compelling reasons to think that Glaxo can actually avoid a sizable dividend reduction. Most significantly, the drugmaker's nascent oncology pipeline has started to show signs of life latly, and its newly approved shingles vaccine is forecast to quickly become a blockbuster product.  

In all, Glaxo's stately yield is far from guaranteed to last, but the company's new management at least seems to be laying the groundwork for a brighter future. 

A bright way to get dividends

Jeremy Bowman (8point3 Energy Partners): The solar sector doesn't usually come to mind when investors think of dividend stocks, as the industry is mostly made up of unprofitable start-ups hoping to break through in the fast-growing renewable energy space. However, 8point3 Energy Partners, a yieldco owned by First Solar (NASDAQ:FSLR) and SunPower (NASDAQ:SPWR), plays by different rules. The company operates a limited partnership that owns, operates, and acquires solar generation projects, and its "primary objective is to generate predictable cash distributions that grow at a sustainable rate." It pays out essentially all of its free cash flow in the form of dividends.

At a current dividend yield of 7.4%, 8point3 should delight income-seeking investors, and it just raised its cash distribution by 3% to $0.2802 per quarter. While the yieldco has traded mostly sideways over the last two years, there is one reason to believe the stock could get a boost. Interest appears to be a building in a sale of 8point3 -- First Solar said it was interested in selling its stake back in April, and SunPower followed suit just a few months after. While it's not clear who the buyer might be, a number of potential parties could come out of the woodwork, including utilities, private equity firms, and pension funds. A sale wouldn't necessarily take the company private, especially if only one stake is acquired, but interest from an operator looking to expand its renewable business could help accelerate 8point3's growth. In the meantime, investors can sit back and collect a fat 7.4% dividend yield.

George Budwell owns shares of Pfizer. Jeremy Bowman has no position in any of the stocks mentioned. Rich Smith has no position in any of the stocks mentioned. The Motley Fool recommends First Solar. The Motley Fool has a disclosure policy.