By Louis Navellier of InvestorPlace

Penny stock investing can be slippery, since many of these low-priced offerings are hard to research. Complicating things is that some penny stocks can be characterized by rapid gains and significant changes in numbers, while others haven't seen their balance sheets budge in some time.So how do you pick good penny stocks? Well since I'm a "growth guy," I only recommend buying stocks with growing sales and earnings. And in my book, there is a very short list of low priced stocks that are seeing sales grow at an impressive rate.

Here they are -- the 8 penny stocks that get my highest rating for "Sales Growth" in my Portfolio Grader stock rating tool:

Comstock Homebuilding (CHCI)

Sector: Household Durables

Market Cap: $28.6 million

Comstock Homebuilding ( CHCI) is a multi-faceted real estate development company engaged in the development of for-sale residential and mixed use products operating out of the Washington, D.C. metro area. Since this time in 2009, CHCI has gained 742.5% on its shares and its largest increase came in April, when it jumped 117% in one week. Coming off consecutive profitable quarters, Comstock could be a good addition to a portfolio at its current $1.78.

Axcelis Technologies (ACLS)

Sector: Semiconductors and Semiconductor Equipment

Market Cap: $180.1 million

The Massachusetts-based Axcelis Technologies ( ACLS) engages in the design, manufacture and servicing of capital equipment for the semiconductor manufacturing industry worldwide. Axcelis provides its services for clients such as IBM, Texas Instruments, and Samsung. Since January ACLS has gone up by 29% and has been showing steady and consistent growth which outpaces its industry rivals, not to mention being half the price with twice the return at $1.83 per share.

Joe's Jeans (JOEZ)

Sector: textiles Apparel and Luxury Goods

Market Cap: $128.3 million

Joe's Jeans ( JOEZ) sources and distributes its branded apparel products to over 1,200 retail doors in the U.S. and abroad with its competitive advantages and industry expertise in denim-wear and denim-related products. The company recently announced a 51% increase in net sales for the quarter ending July 15. With stock already showing an increase in return of 237.7% from the same time last summer, JOEZ might turn out to be a steal at its current asking price of $2.06.

Renhuang Pharmaceuticals (CBP)

Sector: Personal Products

Market Cap: $74.5 million

Renhuang Pharmaceuticals ( CBP) is a developer, manufacturer and distributor of botanical products, bio-pharmaceuticals and traditional Chinese medicines. Renhuang's key product line is the Siberian Ginseng (Acanthopanax) based product series, a natural medicine effective in treating depression, melancholy and other nerve regulating products. Shares of CBP are currently trading for just more than $2 which marks an approximate 100% increase in the past six months.

Camtek (CAMT)

Sector: Semiconductors and Semiconductor Equipment

Market Cap: $70.8 million

Camtek ( CAMT) designs, develops and manufactures automated optical inspection (AOI) systems used to enhance both production processes and yields for manufacturers in the printed circuit board industry, the integrated circuit substrate industry, and the semiconductor manufacturing and packaging industry. CAMT shares trading around $0.78 in July 2009 are trading now at $2.58 per share, a 230.8% increase. With large orders continuing to roll in for the Israeli company, considering an investment in Camtek might be a smart move.

SMTC (SMTX)

Sector: Electronic Equipment Instruments and ComponentsMarket Cap: $39.8 million

SMTC ( SMTX) is a provider of electronics manufacturing services, including product design and sustaining engineering services, printed circuit board assembly, enclosure fabrication, systems integration and testing services, and configuration to order. Investors have enjoyed the ride with SMTX stock so far this year as it has gone up in value 100% since the beginning of March. After announcing a new partnership with FEI, a provider of electron and ion-beam microscopes and tools for nano-scale applications, SMTX is worth a second look at its current $2.76 trading price.

LTX-Credence (LTXC)

Sector: Semiconductors and Semiconductor Equipment

Market Cap: $412.6 million

LTX-Credence ( LTXC) designs, manufactures, markets and services ATE solutions that address the divergent test requirements of the wireless, computing, automotive and digital consumer market segments. Semiconductor designers and manufacturers worldwide use its equipment to test their devices during the manufacturing process. The past three months have brought many sharp rises and falls for LTXC but none seem to overshadow the fact that shares are up 59% since January 2010.

Abraxas Petroleum (AXAS)

Sector: Oil Gas and Consumable Fuels

Market Cap: $222.6 million

Abraxas Petroleum ( AXAS) is an independent energy company primarily engaged in the development and production of oil and gas. The past year has been favorable for investors who were lucky enough to buy AXAS shares this time last summer when they were less than $1. Now that it's nearly two dollars later and shares are at $2.96, the possibility of seeing an investment increase by more than 200% in one year might be enough to lure in some new investors who are hungry for returns.

As of this writing, Louis Navellier did not own a position in any of the stocks named here.

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