Some stocks are one-hit wonders, making a big splash when they first appear, then quickly fizzling into obscurity or oblivion. But for other stocks, that initial big move is only a preview for even bigger and better gains to come.

Today, we've compiled 10 stocks that made some of the biggest upward moves over the past month. We'll then pair that list with the ratings issued by our Motley Fool CAPS community. The higher each stock's rating, the greater CAPS members' faith in that company's ability to keep on beating the market.


30-Day % Change

CAPS Rating

Vonage (NYSE:VG)



Helicos BioSciences



Energy XXI



Sinovac Biotech






PMI Group



ATP Oil & Gas



American International Group (NYSE:AIG)



Ambac Financial (NYSE:ABK)



Huron Consulting (NASDAQ:HURN)



30-Day % change from Aug. 15 to Sept. 15.

As the markets whipsaw to changes in consumer sentiment, there will be weeks like this one where we see gains that are exceptionally ahead of the pace of the movers and shakers of prior weeks. So before we get shaken out again, let's see why the CAPS community thinks some of these companies might continue to outperform the market.

A mighty temblor
Operator, I need to place a call to reality because Vonage is off the hook! Investors bid up shares of the VoIP innovator on the idea that perhaps, maybe, finally the Internet-based phone call service had finally arrived and it would survive the recession.

Vonage only broke into profitability earlier this year by the thinnest of margins, but this surge of strength seems completely misplaced. It can ill-afford at this time to have well-financed competitors like Google (NASDAQ:GOOG) Voice or Skype (if eBay (NASDAQ:EBAY) really does take it private) steal more customers that might otherwise be theirs. It needs every caller it can ring up.

Sure, there's a reduced-cost calling plan from Vonage that features unlimited international calling, and a new iPhone app that may increase interest, but how long will it be able to compete on price? There might be good reason that CAPS member jmc268 thinks this is the beginning of the end for Vonage and it may be "bankrupt before the end of this pick."

Am-backed against the wall
It wasn't too long ago that CIT Group was shaking things up only to have its balloon burst when it announced it couldn't make interest payments on its loans. Now other second-tier financial stocks like Ambac Financial have reenacted similar rise and swoon scenarios, but there's no cause for this penny stock to have made such a move higher.

Analysts say Ambac and fellow monoline insurer MBIA face a looming liquidity crisis in the years ahead because their bond insurance business continues to sustain losses, while they're able to gain scant new business.

Hope springs eternal, though, and CAPS member DomingoMingo believes that if Ambac can survive the current turmoil "every other institution will jump in" once it posts a profit.

Similarly, RomanTheMando says he's got time to wait for Ambac to fix its many problems, after which the bond insurer will be an "even stronger and bigger competitor."

Shake, rattle, and roll
With these stocks shaking the market this past month it pays to start your own research on them at Motley Fool CAPS. Read a company's financial reports, scrutinize key data and charts, and examine the comments your fellow investors have made -- all from a stock's CAPS page.

Try any of our Foolish newsletter services today, free for 30 days.

Fool contributor Rich Duprey does not have a financial position in any of the stocks mentioned in this article. You can see his holdings here. You can shake, rattle, and roll The Motley Fool's disclosure policy, but it still won't break.