The S&P 500 (SNPINDEX:^GSPC) includes 500 of the biggest companies in the U.S., and the vast majority of them pay dividends to their shareholders. But even with the S&P 500 representing the cream of the crop of corporate America, some dividend investors prefer to focus only on the biggest of the index's constituents in an effort to avoid the unpleasant surprises that smaller companies are sometimes prone to give their shareholders. With that in mind, let's take a look at the four top-yielding members of the S&P 100 index, which represents the truly megacap members of the S&P 500.

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4 solid dividend stalwarts
Topping the list is well known Dow component AT&T (NYSE:T), with a yield of 5.4%. AT&T has a long history of rewarding its shareholders with hefty dividend payments, using the immense cash flow that its landlines generated for decades and that its wireless network now provides to give investors solid, dependable income. Even with AT&T returning so much of its capital to shareholders, the telecom giant keeps plenty of cash on hand to build out its network further and take advantage of growth opportunities as they arise -- an increasingly important strategy given the rising competition in the space.

Altria Group (NYSE:MO) is the next high-yielding dividend stock, with a yield of almost 5.2%. The tobacco giant has struggled to grow in recent years, with trends toward reduced cigarette smoking in the U.S. and with the company's business now limited to domestic tobacco after its spinoff of Philip Morris International several years ago. Yet Altria continues to make the most of its leadership role in the tobacco industry, working to navigate through increased regulation and looking for potential growth in electronic cigarettes and other innovations that could lead to a rebound in sales in the future.

The next two companies on the high-yielder list are both utilities, although they've come at the industry from dramatically different directions. Southern (NYSE:SO) is more of a traditional utility, with a diversified mix of power plants using various types of fuel to generate electricity. In recent years, low natural-gas prices and increasing regulation on coal-fired plants have led Southern to make a huge shift in its portfolio of power plants. Southern has moved forward on several fronts, including building new natural-gas plants, building a so-called "clean coal" gasification plant, and seeking new nuclear capacity in an effort to avoid the environmental-compliance costs involved with traditional coal-fired plants. Even with huge capital budgets, Southern has maintained a 4.9%.

Meanwhile, Exelon (NYSE:EXC) yields 4.5%, with much more reliance on nuclear power. That gave Exelon a huge competitive advantage until cheap natural gas came around, as the predictable low-cost nature of nuclear power generation gave it the ability to keep costs stable even in volatile markets for fossil fuels. But even as cheap natural gas has threatened that competitive advantage, Exelon hasn't made big moves to reduce its reliance on nuclear power, instead choosing to use a hedging strategy to protect itself from adverse industry trends. The upside of that strategy is protection from further low prices in electricity rates, but the cost is that it will reduce Exelon's ability to profit when rates recover.

Telecoms, utilities, and tobacco have long been among the highest-yielding industries in the stock market, and it's no surprise to see these blue-chip companies among the top yielders in the S&P. Even the largest companies have some dividend risk, but these four companies could continue to have impressive yields well into the future.