There are no shortage of ways to make money on Wall Street. For the past 12 years, investing in growth stocks has been a moneymaking strategy. Historically low lending rates and an accommodative Federal Reserve have allowed fast-paced companies to thrive.

But over the very long run, few investing strategies have been more lucrative than buying dividend stocks.

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Dividend stocks have vastly outperformed non-dividend payers

Back in 2013, J.P. Morgan Asset Management, a division of JPMorgan Chase, released a report that compared to performance of publicly traded companies that initiated and paid a dividend between 1972 and 2012 to stocks that didn't pay a dividend over the same period. The result? The dividend-paying companies generated an average annual return of 9.5% over four decades, which compared quite favorably to the measly 1.6% annualized return for non-dividend-paying stocks.

These results aren't all that surprising. Companies that pay a dividend are almost always profitable on a recurring basis and time-tested. They typically also have clear long-term outlooks and expect growth to continue.

The biggest challenge for income investors is balancing yield and risk. Ideally, income seekers want the highest yield possible with the least amount of risk. Unfortunately, studies have shown that risk tends to correlate with yield once you hit high-yield territory (around 4%). Since yield is a function of payout relative to price, a company with a failing business model and a plunging share price can offer a high, but potentially unsustainable, yield.

But there's good news, income investors. There are three ultra-high-yield dividend stocks -- I'm arbitrarily defining this as a yield of 8% or higher -- ripe for the picking that can investors can buy hand over fist in December.

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AT&T: 9% yield

The first ultra-high-yield income stock begging to be bought in December is telecom giant AT&T (T -0.82%). AT&T offers a market-crushing 9% yield (which I'll have more to say about in a moment) and recently had its share price hit a more than decade low. That makes it ripe for the picking in more ways than one.

The clear and obvious catalyst for AT&T has always been the rollout of 5G infrastructure. It's been a good decade since consumers and businesses have been offered a significant improvement in wireless download speeds. Although AT&T is spending big bucks on 5G infrastructure upgrades, it'll prove well worth it over the long run. We should expect 5G to encourage a multiyear device replacement cycle that leads to a steady increase in data consumption. Since data is what boosts the company's wireless segment, 5G represents a healthy dose of sustainable organic growth for AT&T.

The other major growth driver for AT&T is the company's pending spinoff of content arm WarnerMedia. AT&T is planning to merge WarnerMedia with Discovery (DISCA) (DISCK) to create a new media entity that'll have more than 85 million pro forma streaming subscribers and offer an even larger library of original content and sports programming. It also doesn't hurt that combining these media behemoths will eventually result in over $3 billion in annual cost savings.

Discovery CEO David Zaslav, who'll head the new company, WarnerMedia-Discovery, believes it could eventually reach 400 million streaming subscribers worldwide.

Additionally, jettisoning WarnerMedia will allow AT&T's remaining business to reduce costs and focus on debt reduction. This'll result a reduction in its dividend payout, likely to around 5%. That's still well above the average yield of the S&P 500, and the historic rate of inflation.

At less than 8 times forward-year earnings, this is probably as cheap as you're ever going to see AT&T get.

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AGNC Investment Corp.: 9.3% yield

Another ultra-high-yield dividend stock income investors can buy hand over fist in December is mortgage real estate investment trust (REIT) AGNC Investment Corp. (AGNC -0.52%). AGNC is currently sporting a 9.3% yield and has averaged a double-digit percentage yield in 11 of the past 12 years.

While the mortgage REIT industry might sound complicated, it's actually pretty easy to understand. Companies like AGNC borrow money at lower short-term lending rates and use this capital to purchase assets with a higher long-term yield. These assets are almost always mortgage-backed securities (MBS). The goal for mortgage REITs is to maximize the difference between the yield from MBSs and its borrowing rate (this is known as the net interest margin). It's really that simple.

One factor that makes AGNC so attractive is the predictability of the mortgage REIT industry. Generally, mortgage REITs perform poorly when the interest rate yield curve is flattening (i.e., the gap between short-and-long-term Treasury bond yields is shrinking), or if the Federal Reserve is making rapid changes to its monetary policy. Conversely, a steepening interest rate yield curve and slow, methodical changes to monetary policy tend to be favorable. Looking back on multiple economic recoveries from a recession, the latter scenario dominates. In other words, we're in that part of the cycle where AGNC's net interest margin expands.

Something else investors should appreciate about AGNC Investment is its focus on agency securities. An agency asset is one that's backed by the federal government in the event of a default. Just $2.1 billion of its $84.1 billion investment portfolio is comprised of non-agency assets.  Though this added protection of owning agency securities does lower the yield it receives on the MBSs it buys, it also allows the company to utilize leverage to increase profits.

With AGNC parsing out a monthly dividend and trading at 12% below book value, it has all the makings of a screaming buy.

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Enterprise Products Partners: 8.4% yield

The third ultra-high-yield dividend stock investors can buy hand over fist in December is oil stock Enterprise Products Partners (EPD 0.65%). This master-limited partnership is paying out a hearty 8.4% yield and is riding a 23-year streak of increasing its base annual payout.

Some of you are probably repulsed by the idea of buying anything having to do with the oil or natural gas industry given what happened last year. The coronavirus pandemic led to a historic drawdown in crude oil demand and pushed oil futures briefly into negative price territory.

However, Enterprise Products Partners was hardly affected. That's because it's a midstream operator of oil, natural gas, and natural gas liquids. Instead of being tied to the wild vacillations of fossil fuel prices, midstream operators are middleman that handle the transmission, storage, and occasional processing of fossil fuels. In this company's case, it has approximately 50,000 miles of pipeline, 19 natural gas processing facilities, and 14 billion cubic feet of natural gas storage capacity. 

The secret sauce for Enterprise Products Partners is its contracts. They're designed in such a way that transmission, storage, and processing volumes are known in advance, which leads to highly predictable cash flow. Being able to craft an accurate annual outlook is imperative to outlaying capital for new infrastructure projects and maintaining the company's superior dividend.

Speaking of which, at no point during the height of the COVID-19 pandemic did this company's distribution coverage ratio -- a measure of annual distributable cash flow relative to what is actually distributed to shareholders -- dip below 1.6. Anything below 1 would represent an unsustainable payout. This demonstrates Enterprise Products' payout is extremely safe, even at an 8.4% yield.

At a multiple of 10 times forward-year earnings, Enterprise Products Partners is downright inexpensive.