It's a good time to think small.

The market has been rallying since mid-March, and low-priced stocks have been some of the bigger beneficiaries. When the risks are high, the rewards usually follow when stock exchanges are percolating.

I have been singling out attractive opportunities since my original "5 Stocks Under $10" eight years ago. The past few months have been exciting times in this space.

Let's go over the five picks from March to prove my point.

 

Sept. 18

March 13

Gain

Sirius XM Radio

$0.6798

$0.198

243%

Bare Escentuals

$11.59

$3.66

217%

Focus Media

$9.43

$5.74

64%

Geron

$7.41

$4.36

70%

Ford

$6.94

$2.19

217%

The average gain of 162% in just six months is remarkable. Sirius XM Radio (NASDAQ:SIRI) and Ford (NYSE:F) have battled back from major challenges and have gone on to more than triple.

Will the next six months be as scintillating? Probably not. The rallying markets are due for a breather, and the same goes for the stocks trading in the single digits that I cover every month. This is a risky fishing hole, and whatever goes up can just as quickly come down.

Let's go over this month's picks.

United Online (NASDAQ:UNTD) -- $8.31
With all of the excitement centering on Facebook's torrid growth, investors seem to forget that one of the original ways of keeping tabs with former schoolmates -- Classmates.com -- is part of publicly traded United Online.

Yes, Classmates blew it. Sticking to its model as a premium subscription service as social-networking speedsters Facebook and MySpace thrived as free hubs of viral goodness was a huge mistake. However, Classmates is closer to taking on Facebook than any other site starting from scratch.

In the meantime, United Online's eclectic collection of companies -- including floral arrangement giant FTD, online loyalty marketer MyPoints.com, and Internet access discounters Juno and NetZero -- combine to generate healthy cash flow and consistent profitability. Analysts see the company generating a profit of $1.34 a share this year, which puts the stock at just six times earnings.

China Finance Online (NASDAQ:JRJC) -- $9.66
The only thing better than dishing out equity research to individual investors is doing exactly that in China. As the world's largest nation continues to take baby steps toward capitalism, demand will increase for market watchers to gain an edge.

The rub of China Finance Online is that it has had to deal with a pair of money-losing quarters this year. Analysts see the company bouncing back next year, making this a timely entry point for contrarians who want exposure in China.

Harris & Harris (NASDAQ:TINY) -- $6.41
Nanotechnology was the meaty buzzword when Motley Fool Rule Breakers originally recommended Harris & Harris to growth-stock subscribers four years ago. As a venture capitalist specializing in "tiny tech," Harris & Harris owns a basket of nanotech upstarts at attractive venture capitalist funding points.

Things have been frustratingly slow to develop with nanotechnology in general and Harris & Harris in particular, but this also gives us a dynamic opportunity to get into the stock before many of its companies go public in the coming years.

Acacia Research (NASDAQ:ACTG) -- $8.94
Acacia acquires, develops, and licenses patents, which can be a pretty lucrative business. The company recently announced that its revenue over the past 12 months was 58% higher than during the previous year.

Acacia isn't profitable on a reported basis at the moment, primarily the result of the amortization of the patents it shrewdly snaps up. But the company is blessed with a debt-free balance sheet and roughly $2 a share in cash. As it continues to milk its intellectual properties -- 100 patent portfolios and climbing -- its cash flow and earnings will keep improving.

Great Wolf Resorts (NASDAQ:WOLF) -- $3.83
Running a pricy chain of earthy lodges with massive indoor water parks doesn't seem like a winning move during a deep recession, but Great Wolf has held up better than you would probably think.

It surprised investors by posting positive EBITDA on an adjusted basis in its latest quarter. Revenue per available room -- a popular metric for the hospitality industry -- dropped 6% in constant dollars, but the hotel industry itself suffered a much steeper decline.

Great Wolf is going to be a big winner once consumers feel they have a little more discretionary income.

Five for the road
These five stocks aren't trading in the single digits by accident. If I'm right about the catalysts, though, they may not be trading in the single digits for too much longer.

Finding promising stocks while they're still cutting their baby teeth is at the heart of the Motley Fool Rule Breakers newsletter that I write for. You can check it out for free with a 30-day trial. There are nearly a dozen active recommendations in the growth stock research service trading for less than $10, including China Finance Online and Harris & Harris. Check those out, and I'll be back with more on the third Monday of next month.

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Longtime Fool contributor Rick Munarriz wonders how many people know that Alexander Hamilton is the one on the $10 bill. He does not own shares in any of the stocks in this article. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.