Take your mind back to the third quarter of 2011. Companies were posting robust profits and investors were wading back into the market, helping to fuel a 15% gain in the S&P 500 from early October to the second week of November.

But the just-ended earnings season must seem like an ancient history now, and investors are once again hitting the “sell” button. Since peaking at 1,278 on Nov. 8, the S&P 500 has already begun to cough up its gains and is now on its way to buckling back under the 1,200 mark.

The sudden mood change must be especially hard to fathom for the companies that just delivered great third-quarter results, since several stocks posted double-digit gains on the day they released earnings. I took a closer look at the stocks that have given up most or all of their gains in subsequent sessions to see what their fundamentals look like for the upcoming quarters. It’s important to keep in mind that the recent price drops these stocks have seen is not their fault. They’re good companies stuck in a lousy market environment.

Here are the five companies I found…

1. Genworth Financial (NYSE: GNW) 
One-day gain: 17%

This insurer saw its shares jump by more than $1 on Nov. 4 to $7.19 after reporting earnings per share (EPS) of $0.21 — two cents ahead of the consensus forecast. Investors were also cheered by news that its Australian unit would conduct a value-unlocking initial public offering (IPO). A few weeks later, shares are right back at $6. The move to conduct an IPO for 40% of its Australian division led Citigroup to boost their rating from “sell” to “neutral.”

“The move could shore up GNW’s balance sheet while simultaneously improving financial flexibility and providing a more ascertainable floor valuation for its shares,” they note along with their $8 price target. This is the same price target used by Merrill Lynch, implying more than 35% upside from current levels.

2. Codexis (Nasdaq: CDXS) 
One-day gain: 24%

My colleague Andy Obermueller has been high on this stock for a while. [It’s one of the top picks in his Fast-Track Millionaire newsletter.]

Third-quarter results pushed this stock from $4.50 to $5.50 on Nov. 2, but it is now back where it started. Codexis provides enzymes that can catalyze biofuel production, but the company’s technology is also being applied to the manufacture of pharmaceuticals. Roughly 40% of current revenue comes from product sales, while the rest is partner-funded research and development (R&D) initiatives (mostly from Shell (NYSE: RDS)). Record third-quarter sales of $31.4 million topped forecasts by about 5%, but as noted, the current market weakness has already made investors take profits. For a fuller explanation of why Codexis is a solid stock, please see my analysis here.

3. Alpha Natural Resources (NYSE: ANR) 
One-day gain: 13%

Solid third-quarter results helped push this coal miner up more than $3 to $27 on Nov. 3, though the stock gave up those gains and another dollar to boot, down to $23. The early November surge came on EPS of $0.35 that topped the consensus forecast by more than 10%. This strength came from a June 2011 acquisition of Massey Energy, which should help push revenue to exceed $8 billion by 2012.

Alpha Natural is especially well-positioned to capture still-rising coal demand in China and should also profit from increased production of metallurgical coal, which is valued for its high-heat content in steel mills. Analysts at Sterne Agee expect shares to move back up to $35 (the stock hit $60 last spring) as Alpha Natural applies a projected $1 billion in free cash flow to stock buybacks during the next two years. This would be a wise use of corporate funds, considering shares trade for three times consensus projected 2013 EBITDA.

4. MedAssets (Nasdaq: MDAS) 
One-day gain: 14%

A stellar third quarter helped boost this stock more than $1 on Nov. 4 to $12, but shares have retreated back below where they stood before results were released. The fact that this health care technology provider topped EPS forecasts by at least 40% for the second straight quarter is a bit deceiving. Some of the gains came from unanticipated accounting factors. Still, MedAssets has solid operating momentum, with sales expected to rise more than 40% this year to about $575 million. 

The company’s suite of services helps hospitals gain operating efficiencies by maximizing potential reimbursement revenue. Merrill Lynch analysts say the company can help a typical hospital boost operating margins by 500 basis points, and this value proposition is why Merrill sees shares nearly doubling to $20.

5.Terex (NYSE: TEX) 
One-day gain: 19%

Shares of this heavy-equipment maker spiked from $15 to $18 on Oct. 27 as a result of robust quarterly sales ($1.8 billion that came in $200 million ahead of forecasts and a $0.30 EPS that beat the consensus estimate by more than 30%).  Management also used the occasion to boost 2011 guidance sharply, from a previous $5.5 billion to $6.4 billion. The company has been out of the spotlight since, and a slowly weakening market has engorged all of those gains.

This is all because of troubles in Europe, where Terex derives 35% of sales. The selloff is partially attributable to concerns that the crises in the region will lead to a very deep recession.  If the worse-case scenario isn’t realized, then this is an extremely inexpensive stock at a recent $15. Analysts expect EPS to quadruple to about $1.65 in 2011 and rise further to $3 by 2013. Trading at five times this forward view puts this stock back into bargain territory. 

Risks to Consider:  These stocks may need to prove themselves again in the next quarter since the recent quarterly results are no longer providing share-price support. 

Action to Take –> When the market stabilizes again, look for investors to revisit stocks that are delivering solid quarterly results. Any of these five names surely fit this requirement and should be considered as solid portfolio candidates for investors.