General Motors car rental service Maven. Image source: General Motors.

From time to time, stocks go on sale. Over the last year, the S&P 500 has remained roughly unchanged, even as the business of many companies has improved. For that reason, investors looking for a bargain have many stocks to choose from. Let's take a look at four promising companies trading at modest valuations.

Western Digital offers an attractive dividend

Shares of hard drive-maker Western Digital (WDC 2.23%) have plunged over the last year, falling more than 50%. At current levels, Western Digital trades with a price-to-earnings ratio around 13 -- far below the broader market. More interesting is Western Digital's strong dividend: the stock yields about 4.27%.

Western digital's core hard drive business is intimately linked to the traditional PC. That's a problem, as PC sales have declined notably in recent years. Replacement cycles have lengthened, while a growing number of consumers, and even some business users, have begun using mobile devices as an alternative.

More recently, Western Digital completed the acquisition of flash storage specialist SanDisk. The purchase was controversial, with some arguing that Western Digital was paying too much. And Western Digital's deal with China's Unisplendour (which would've seen the investment firm acquire 15% of the hard drive-maker) fell apart.

But Western Digital's business is increasingly diverse. Nearly two-thirds of Western Digital's revenue last quarter came from sources other than the PC. The integration of SanDisk will further diversify Western Digital, and boost its sales by around 30%. SanDisk is a major player in the market for solid state drives, a technology that's slowly chipping away at the demand for hard drives. It also adds increased exposure to mobile devices.

General Motors pays even more

Automotive giant General Motors (GM 1.35%) boasts an even more impressive dividend than Western Digital, yielding 5.23% at current levels. GM declared its first post-bankruptcy dividend in Jan., 2014, and has since raised it two times. At the same time, however, GM shares have lost more than 27% of their value. GM's trailing price-to-earnings ratio has contracted, and it currently hovers in the low single-digits.

Fears of a bubble in subprime auto lending have taken a toll on GM's stock, along with longer-term concerns about its fundamental business model: In an era of self-driving, electric automobiles, can the ancient Detroit automaker survive? But GM hasn't shied away from innovation, investing in Lyft, acquiring Cruise Automation, and building long-range electric vehicles of its own.

Last quarter, GM's North American business was solidly profitable, and its European business broke even. For 2016, the company expects to generate free cash flow of nearly $6 billion.

Intel's PC business has struggled, but its other units have grown

Chip giant Intel (INTC 1.74%) faces similar challenges to Western Digital. With so much of its business tied to the PC, declining shipments have weighed on investors. Over the last 12 months, Intel shares have traded in a tight range, and the stock is basically unchanged from last June, despite the fact that the company's revenue and net income have risen. Last quarter, Intel generated $13.7 billion in revenue and $2 billion in net income, up 7% and 3%, respectively. Intel currently trades with a 13.45 PE and offers investors a 3.25% dividend yield.

Intel derives the bulk of its revenue from its Client Computing Group, which is largely composed of the processors it sells to power traditional desktop and laptop PCs. Last quarter, client computing revenue rose just 2% on an annual basis. But other portions of Intel's business are growing much faster. Notably, its data center business saw its revenue rise 9% on an annual basis, and its Internet of Things and security revenue rose 22% and 12%, respectively.

If the market for traditional PCs rebounds, Intel investors could be rewarded. Even if it doesn't, growth in its other segments could benefit shareholders over the long-run.