Market volatility has recently moved to multi-year lows, leading to investor complacency. But it’s time to sit up and pay attention again: the Dow Jones is registering its third straight session of 150-point swings. That’s great for day traders and options players, but nerve-wracking for the buy-and-hold crowd.

But there’s a silver lining. The intra-day weakness is masking some very strong results, muting stock performance gains. When the market has a quieter day, these stocks could power higher. However, there are a handful names that have managed to spike far higher today, even as the major indices stumble.

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For many retailers, it’s easy to post big profits during the holiday season, but the other three quarters can see losses mount. The challenge is to generate profits in those seasonally slower quarters, which Overstock.com (Nasdaq: OSTK) has just done. The e-tailer posted first-quarter results that were far ahead of forecasts, pushing shares up more than +15% to an 18-month high. The results were so strong that analysts may need to double their 2011 profit outlook from the current consensus of $0.57 a share.

#-ad_banner-#The key question is whether the company’s impressive 42% spike in sales is a harbinger of more strong quarters, or the result of heavy promotions. A 200 basis-point compression in gross margins tells you that pricing was sacrificed to move the goods. But the swing to profitability is an undeniable positive.

More than likely, this sales momentum is for real, and there is a chance that growth could become viral. E-tailers depend on critical mass, and strong word-of-mouth. Overstock has the critical mass in place, and could start to become a regular destination for bargain hunters.

Shares appear reasonably priced at around 20 times likely 2011 profits (which as noted, could be far above the current consensus). More important, moderate sales growth could yield profit growth rates well higher than that price-to-earnings ratio (P/E), as e-tailers have a tremendous amount of operating leverage. Even as shares are hitting fresh highs, they should garner new growth-seeking investors.

 
 
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Shares of NutriSystem (Nasdaq: NTRI), which had lost half of their value over the last five months, are back on the upswing today, posting a +20% gain. The purveyor of diet supplements boosted marketing efforts to woo new customers. And that paid off handsomely, as sales grew even faster than those rising expenses.

But investors need to temper their enthusiasm, as this industry has fully matured and represents very few growth prospects. Shares at about 17 times next year’s profits are no bargain.

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Executives at Cardinal Health (NYSE: CAH) must be kicking themselves. They decided to spin off the company’s CareFusion division “to unlock shareholder value.” But CareFusion (NYSE: CFN) is now posting moderate growth at a time when Cardinal is set for flat growth in fiscal 2010 ending in June. Shares of CareFusion are up another 5% today, and are up more than 70% since last summer’s spin-out.

Shares of Cardinal have also risen, albeit at a lesser pace. And although CareFusion may have snared recent plaudits, Cardinal health may be the better play in the quarters ahead. I wrote about Cardinal Health’s turnaround efforts in this piece in February.