The stock market proved today just how volatile it can be, with a good start related to progress in Europe in resolving the Greek sovereign debt crisis then giving way to concerns about the U.S. economy. In particular, home prices fell in 19 of 20 major city markets, and consumer confidence dropped unexpectedly. Just after 2 p.m. EST, the Dow Jones Industrials (INDEX: ^DJI) were down 59 points to 12,595, while the S&P 500 (INDEX: ^GSPC) fell four points to 1,309.

Earlier today, Fool analyst David Williamson covered earnings news from ExxonMobil and Pfizer, which sent both stocks lower. But other Dow stocks were also noteworthy.

American Express (NYSE: AXP) bucked the downtrend, climbing 1.5% in early afternoon trade. The company led the entire Dow financial sector higher, as stability in Europe is arguably more important at least in the short run than the mixed economic news that has been so prevalent recently.

Wal-Mart (NYSE: WMT) lost about 1%. The leading bricks-and-mortar retailer is in the spotlight as Amazon.com announces earnings after the market close this afternoon. With online retail gaining in popularity, long-term investors are concerned that Amazon could continue to poach business away from Wal-Mart and other big-box retailers -- despite Wal-Mart's increasing presence online with its own website.

Finally, Intel (Nasdaq: INTC) also dropped just over 1%. As Intel begins to push into the mobile chip market, the company's rivalry with ARM Holdings (Nasdaq: ARMH) will inevitably heat up. Already, ARM has started to push into the PC market in response, to go up against Intel on its home turf.

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