Sales of accessories for portable digital players are soaring as the gadgets become the latest craze in take-along technology.

U.S. retail sales of accessories such as cases, speakers and car kits more than quadrupled in the first nine months of 2005 to $412 million from $87.3 million in the year-ago period, according to the latest data from the NPD Group research firm.

With that kind of momentum, the industry is poised to rake in more sales in the holiday-filled fourth quarter than it did during the first three quarters, approaching $1 billion for the entire year, NPD analyst Steve Baker said.

"Accessories — it's not just throwaway stuff anymore," Baker said.

Meanwhile, sales of portable digital players, led by the phenomenal popularity of Apple Computer Inc.'s iPod, soared to more than $1.6 billion in the year's first nine months — up 163 percent, from $581.3 million last year.

The 370 percent surge NPD tallied in accessory sales doesn't take earphones into account. NPD does not include them because of the difficulty in determining whether the items were purchased for use with other devices such as cell phones, Baker said.

Speaker systems for portable players topped the accessory category, generating $109 million in revenue, followed by cases and bags, which brought in $73.1 million. FM transmitters were the third most lucrative at $64.5 million. Next came car kits, which generated $29.1 million and FM modulators/car chargers, which brought in $28.8 million in revenue, NPD said.

Driving the sales were Apple's line of iPods, which has more than a 70 percent share of the digital player market.

"It's all part of the iPod economy," Baker said.

Among the manufacturers reaping the most from the accessories boom were Apple, Digital Lifestyle Outfitters, Griffin Technology Inc., Bose Corp., Altec Lansing Technologies Inc. and Harman International's JBL company, according to NPD.

Retailers are also well aware of the skyrocketing business. In time for the holiday season, RadioShack Corp. last week started selling iPods, giving the trendy gizmos and many of its accessories a prominent, dedicated section inside more than 5,000 of its stores.