Have you ever had a "case of the Mondays"> Well, the S&P 500 (SNPINDEX:^GSPC) certainly does today, with no economic news and relatively few earnings reports moving the market. Overall, the broad-based index has been vacillating within a very tight four-point range as modest profit-taking pushed the index slightly lower throughout the session. On the day, the S&P 500 finished fractionally lower by 0.92 points (-0.06%) to close at 1,517.01.

However, today's tiny move meant little for three companies within the index that had noticeably stronger moves higher. Here's a glimpse at today's three best stocks within the S&P 500.

Solar-module manufacturer First Solar (NASDAQ:FSLR) once again found itself atop the biggest gainers, with a 6.5% move higher. While no specific news on First Solar sent the company higher, a mixture of soft guidance from SunPower last week, coupled with the continued pricing struggles of Chinese solar manufacturers, leads investors to believe that First Solar is picking up momentum and market share. First Solar has had moderate success in landing large projects in the U.S. in recent months, and that could translate into at least some near-term cash flow stability.

Credit rating agency McGraw-Hill (NYSE:SPGI), and even its peer Moody's (NYSE:MCO), are rallying 4% and 5%, respectively, after taking a nasty tumble in the prior week. According to a report from The Wall Street Journal, the reason the U.S. Department of Justice didn't go after Moody's in its $5 billion lawsuit against Standard & Poor's (a division of McGraw-Hill) is that it didn't leave a blatant email paper trail like that which was found at S&P. The rally from Moody's looks strictly like a sigh of relief that it's unlikely to be charged with any wrongdoing. As for McGraw-Hill, the rally today could be from investors who realize that many of these lawsuits are settled out of court for much less than the DOJ is seeking. Having shaved $5 billion in market value off its share price already, the move lower in McGraw-Hill's share price might be a big overreaction.

Finally, railroad operator CSX (NASDAQ:CSX) jumped 3% after a Barron's article over the weekend spoke optimistically of the company's prospects. Cited in the article was a mixture of stabilizing coal prices and tight cost controls, as well as share repurchases, which stand to benefit CSX's bottom line. Two points that I wouldn't forget about are (1) CSX's steadily growing dividend that earned it the designation as a great dividend stock you can buy right now from me, and (2) its roll in coal exports. Speaking of the second point, coal companies are turning to exports to stabilize production demand, and CSX should see an increase in rail demand as a result. I don't always agree with Barron's, but in this case I think they've hit on some key growth drivers for CSX moving forward.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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