As my colleague Mike Turner has noted, September was one for the record books. [Read Mike’s article here]

And as Mike notes, it never hurts to play a little defense after such a good run. But in these markets, you’ll need to stay nimble. Coming earnings reports may just be good enough to keep the markets moving north, forestalling the moment when profit-taking dominates the action.

With that in mind, let’s look at three companies that will report quarterly results in the next week or so. What they have to say about business conditions may well set the trading tone for the rest of October and beyond.

Aloca (NYSE: AA)
On the first Monday in October, the Supreme Court kicks off a new term. And a few days after that, Alcoa always kicks off earnings season. For the past few years, Alcoa has set a somber tone as global demand for aluminum has been in a slump ever since Europe and the United States headed into the downturn. Yet I recently opined that a turn may be coming for Alcoa. [Read: “The Best Rebound Play in the Dow”]

That turn is likely to be in evidence in 2011 and even more noticeably in 2012. But what about right now? Well, expectations are low, and that’s a good thing. On Monday morning, Deutsche Bank downgraded Alcoa to a short-term sell rating. (Curiously, Deutsche Bank’s target price was reduced from $18 to $15.50 which is still roughly +30% above current prices. And their analysts lowered their 2011 EPS forecast from $1.50 to $1.29, which is still well above the $1.01 consensus EPS estimate).

There is little that Alcoa can say to rattle the market as investors expect demand and aluminum pricing to stay weak for at least the remainder of 2010. But as I noted a few weeks ago, output of aluminum has been very restrained, and as a result, the London Metals Exchange (LME) reports that inventories now sit at a 52-week low. The market is already reflecting tighter supply: the spot aluminum price has risen from $1,900 per ton in June to a recent $2,330 (though it remains roughly $1,000 per ton lower than the 2008 peak).

Demand remains well below 2008 levels, but so does supply. So there’s no reason that prices can’t move back toward the $3,000 mark — as long as the industry maintains its current production discipline. On this Thursday’s conference call, give a close listen to management’s discussion of output. As the world’s biggest supplier of aluminum, Alcoa can set the tone for supply — and pricing.

Supply, demand and pricing are key concerns for all kinds of metal producers. The market dynamics in aluminum apply to steel and copper as well, and as noted in this article, many metals producers sport very low P/E ratios.

Intel (Nasdaq: INTC)
This technology bellwether has given investors whiplash this summer. In mid-July, Intel released solid second quarter results and CEO Paul Ottelini told investors that “in Q2, we saw the return of corporate purchases,” adding that industry had finally moved past the 2009 downturn. “The difference is that corporations are buying now in addition to consumers,” Otellini said at the time. Well, six weeks later, Intel had a change of heart, lowering third quarter revenue forecasts by about $600 million. “Revenue is being affected by weaker-than-expected demand for consumer PCs in mature markets,” said Intel in late August. Shares now languish just above the 52-week low.

Even as shares appear cheap at less than 10 times projected 2010 profits, there may be little management can do to get the stock moving on next Tuesday’s conference call. After the Jekyll-and-Hyde commentary from earlier this summer, few investors would believe the company if it spoke in bullish terms. And therein lies the opportunity for tech stocks. Investors now have ample time to digest earnings reports and look for the best tech names to own, as sector shares are unlikely to see heavy buying in coming weeks, no matter how strong earnings results and outlooks are.

That’s not to say that tech stocks are unattractive, they just aren’t timely. Yet many large tech stocks are trading at very cheap multiples. [See: “This Sector’s Mountain of Cash Could Soon Line Your Pocket”]

And if a so-so earnings season makes these stocks any cheaper, then value investors will queue up to buy shares while they are at generational lows. Equally important, it’s too soon to conclude that 2011 tech spending will be lousy, even if share prices seem to anticipate that. This is an industry where the reward seems far greater than the risk, even if no near-term catalysts exist. (If you’re a tech investor, you should also check out Micron Technology’s (NYSE: MU) results, which will be released on the same day.)

CSX Corp. (NYSE: CSX)
On the same day that Intel and Micron report, freight carrier CSX will also weigh in. Freight volumes are a key tell for investors trying to gauge the economic activity in the economy. Analysts expect CSX to report a +16% jump in revenue from a year ago, which should lead to a +40% spike in profits, thanks to impressive operating leverage. But investors should know that the easy gains may be winding down and the year-over-year comparisons in future quarters may be far less robust, as CSX’s results already started to turn up nicely last fall.

Shares have made a solid +15% upward move since late August and aren’t much of a bargain right now. So the key here is to see what CSX has to say about the broader economy. If freight volumes are off to a solid start in the fourth quarter, that’s a good omen for the U.S. economy as a whole.

Action to Take –> The conference calls for Alcoa, Intel and CSX will tell a great deal about the current state of economic activity — pay particular attention to them even if you’re not considering these stocks for your portfolio. Alcoa and Intel are deeply tied into global trends, while CSX is more focused on North American activity. With the economy appearing to wobble on the fine line between modest growth and modest contraction, these companies’ outlooks will surely set the tone for the entire earnings season.