By Katie Marsal

Published: 10:00 AM EST

Although Macs and iPhones were seen as Apple's ticket to a healthy holiday quarter, the electronics maker has reportedly been struck by surprising demand for iPods and is now scurrying to restock some of its reseller channels.

"What started out as stock outs on the iPod touch at Amazon.com from Black Friday is starting to spread to other retailers and iPod models," said Kaufman Bros. analyst Shaw Wu, who drew attention to the sudden shortages in a report to clients earlier this week.

He notes that Amazon.com, one of Apple's highest volume iPod resellers, has just recently pushed lead times on the 8 GB second-generation iPod touch to three to five weeks from 11 days while the 16 GB model remains at three to five weeks.

In addition, the analyst's distribution and channel checks show that the iPod touch, iPod nano, and even iPod shuffle are seeing spotted shortages on different colors and capacities this week across several retailers including Best Buy, Target, Wal-Mart, and Crutchfield.com.

"Frankly, we find these sell-outs on iPods surprising given how difficult the macroeconomic environment is, putting a crimp on consumer spending," he told clients in a new report Wednesday. "From our assessment, we believe iPod is holding up better than most, due to its relatively low [selling price] and strong consumer understanding of the value it provides."

Despite concerns that iPods may be approaching a saturation point in the consumer market, Wu said the players' recent momentum gives him confidence in his estimate that Apple will sell around 21 million of the devices during its December quarter.

That would represent a 90% increase over the company's September quarter iPod sales and a mere 5 percent decline from last December quarter when sales hit an all-time high of 22.12 million units.

Wu, who maintains a Buy rating on Apple shares, continues to believe the Cupertino-based company is one of the better investments during the tough economy given its strong fundamentals.

"We find the risk-reward favorable for longer-term investors at 12x our calendar 2009 free cash flow (FCF) estimate," he said. "We see upside to our price target of $120 based on a conservative 15x multiple."

Note: While Amazon.com continues to reflect availability of the 8GB and 16GB second-generation iPod touch, sales of those devices are being channeled through its affiliate partners and are not a reflection of its own inventories. As such, iPods continue to dominate the top 13 spots on the retailer's Top Sellers list of MP3 players, helped by discounts of between 8% and 38% on third- and fourth-generation iPod nanos.