(MONEY Magazine) – If you shop at Wal-Mart (WMT), you may not notice that thousands of items on its shelves are actually store brands. "Private label" products such as Ol' Roy dog food, White Cloud toilet tissue, Faded Glory jeans and Great Value foods are an estimated 40% of Wal-Mart's sales, according to Private Label magazine. That adds up to about $100 billion. For some niche players who make these cut-price products, that's a big opportunity. There are risks to being closely tied to one retailer, but the advantages include simpler distribution and inventory control, access to Wal-Mart's huge customer base and minimal need for advertising. Here are three stocks, all with market caps between $1 billion and $2 billion, that have latched on to Sam Walton's growth machine:

Cott (COT; $27) is the top maker of store-brand sodas, including Wal-Mart's Sam's Choice, which accounts for some 40% of Cott's sales. It trades at 21 times estimated 2004 profits.

Perrigo (PRGO; $16) is the dominant player in discount knockoffs of over-the-counter remedies. Its sales at Wal-Mart, under the popular Equate brand, were 27% of its $826 million sales. Its P/E is 21.

Regis (RGS; $39) is the world's largest haircut chain, with nearly 10,000 salons, and it has a P/E of 17. It's getting a boost from its SmartStyle shops, located only in Wal-Mart megastores. --AMY FELDMAN