These little-known companies have been growing rapidly and are still worth considering for your portfolio. By Kathy Kristof, Contributing Editor November 2, 2012 Virtually every investor has heard about Apple (symbol AAPL), the Cupertino, Cal., tech phenom that doubled in value over the past two years and is now the world's biggest company by stock market capitalization. But did you know that the shares of a little fertilizer company based in Newport Beach, Cal., have trounced Apple's?SEE ALSO: The Slide Show Version of This Story That's right. While the shares of Apple, at $597, have roughly doubled since October 2010, the shares of American Vanguard (AVD) have soared by about 400% over the same period. So, if you had invested $1,000 in Apple two years ago, your investment would be worth $1,844 today; if you had invested the same amount in American Vanguard, it would be worth $4,290. Of course, with just $304 million in sales (compared with Apple's $108 billion), the company is just a fraction of Apple's size. American Vanguard and many small companies like it fly under the radar of the vast majority of investors. Typically, few analysts cover these companies, so they're tough to ferret out. We've dug up six little-known outfits that have been growing at a heady pace, in terms of both profits and share price, and are still worth your consideration. (All share prices are as of the November 1 close.) Advertisement 1. Technology and drug companies use patent protection to keep competitors at bay for decades. But Acacia Research Corp. (symbol ACTG) has managed to turn buying and licensing patented ideas and formulas into a stand-alone business -- and a highly lucrative one at that. Rather than develop patents itself, the company -- which, like American Vanguard, is based in Newport Beach -- partners with patent holders to prosecute violations and protect their inventions from unauthorized use. Acacia now controls 200 patent "portfolios" covering thousands of inventions. Analysts note that patent revenue can be "lumpy," varying by wide amounts each year. But the lumps have been pretty impressive this year. During the first six months of 2012, Acacia earned $1.19 per share, compared with 37 cents per share during the same period a year ago. Analysts expect earnings to soar 383% in 2012, to $2.43 per share. At $25.48, Acacia sells for just 10 times estimated 2013 profits -- a screaming bargain for a company that, analysts say, can generate earnings growth at an annual clip of 38% over the next five years. 2. Making pesticides and insecticides may not sound like an exciting business, but American Vanguard (AVD) has made it plenty profitable. The company earned 79 cents per share, or $22.1 million, in 2011 -- double the profits of the year before. During the first six months of 2012, profits jumped another 59%, to $17.5 million, or 61 cents per share. Analysts expect double-digit growth for the next two years at least. Advertisement The reason: American Vanguard has a virtual lock on the market for some pesticides that have proven particularly effective in combating rootworm, the current scourge of corn farmers. The company also has a delivery system -- the "smart box" -- that reduces farmers' exposure to the toxic chemicals they must apply to the soil to kill the bug. Eventually, chemical companies may come up with genetically engineered seeds that are better resistant to pests, but that could take years. In the meantime, analysts project, American Vanguard's earnings should grow at a blistering 30% annual pace over the next few years. At $32.81, the stock sells for just 22 times estimated 2013 earnings of $1.52 per share, a reasonable price-earnings ratio in light of expected earnings growth. Gabelli & Co. analyst Amon Wilkes believes the stock will sell for $43 by the end of 2014. 3. Air Methods (AIRM) is a company that provides medical transportation services. It specializes in using helicopters to pick up severely injured or ill patients and take them to trauma centers. The company, launched in the 1980s and based in Englewood, Colo., went public in 1991. Since then, it has purchased a series of competitors and has been growing at a breakneck pace. In the first half of 2012, revenue jumped 48%, to $222.5 million, from the year-earlier period, and profits more than doubled, to $44 million, or $3.39 per share. The stock, at $108.08, sells for 16 times projected 2013 earnings of $6.82 per share. That looks like a good price, considering that analysts expect Air Methods to generate annual earnings growth of 17% over the next three to five years. Advertisement 4. Auto parts maker Dorman Products (DORM) has benefitted mightily from the proliferation of old cars needing replacement parts. During the first half of 2012, the company posted a 13% gain in revenue and a 21% jump in profit. In an upbeat second-quarter earnings release, the Colmar, Pa., company attributed the heady gains to demand for newly introduced products. Meanwhile, Dorman's administrative expenses dropped as a percentage of revenue, allowing the company to boast an enviable 37% gross profit margin (revenues minus cost of sales, divided by revenues). Few analysts cover Dorman -- not surprising, given that annual sales are less than $300 million -- and there are no long-term earnings projections for the company. But all three of the analysts who do follow the stock have "strong buy" recommendations. With a history of double-digit earnings growth, Dorman may be worth a look. The stock, at $33.18, sells for 16 times projected 2013 profits of $2.13 per share. 5. Liquidity Services (LQDT) is government and industry's answer to eBay. The Washington, D.C., company operates a number of online auction sites, such as Govdeals.com and www.govliquidation.com, that the Department of Defense and other government agencies use to unload scrap and other assets that are no longer needed. In July, Liquidity acquired GoIndustry, which sells assets for dozens of manufacturing companies located all over the world. In the quarter that ended June 30, revenues were up 46% from the year-earlier period, while adjusted net income (which excludes stock compensation and acquisition costs) rose 122%. The company says it's benefiting from government cost cutting, as well as from Americans' growing cost-conscious mentality, which has everyone looking for bargains. At $41.87, the stock trades for 19 times estimated 2013 earnings of $2.19 per share. With analysts estimating long-term earnings growth of 30% a year, Liquidity shares look like a good deal. Janney Capital Markets analyst Shawn Milne rates the stock a buy and has a one-year price target of $67. Advertisement 6. At On Assignment (ASGN), job one is to find people jobs. But the Calabasas, Cal., staffing company isn't looking for just any jobs. It finds positions for doctors, nurses and engineers. That's important, says Deutsche Bank analyst Paul Ginocchio, because health care and technology are businesses likely to grow even in a stagnant economy. And On Assignment appears to be capturing a growing percentage of the business. That should keep the company's earnings growing at a double-digit rate for the next three to five years. The company is also well managed, bringing an increasing amount of revenue to the bottom line. At $19.72, On Assignment sells for 16 times projected 2013 earnings of $1.24 per share. That's only 6.5% below the $21 one-year target price that Ginocchio set for the stock when he first started covering the company in July. Nonetheless, he continues to rate the stock a buy. Kathy Kristof is a contributing editor to Kiplinger’s Personal Finance and author of the book Investing 101. Follow her on Twitter. Or email her at email@example.com. Kiplinger's Investing for Income will help you maximize your cash yield under any economic conditions. Subscribe now!