Apple is expected to unveil new iPods this week, injecting fresh excitement into the product line at a time when defections by partners have shown cracks in its digital music dominance.

Apple has not revealed what Chief Executive Steve Jobs will announce at a Wednesday event in San Francisco, but analysts are betting on an iPod with a large touchscreen and a new form for the smaller iPod Nano.

There is also speculation that Jobs could pull a surprise out of his sleeve and show off iPods with the ability to buy and download music wirelessly, or finally announce the addition of the Beatles' music catalog to the iTunes online store.

It may be more important than ever for Apple to keep its market-leading grip on music players as it finds its iTunes store increasingly under fire from content partners like NBC who are unhappy with how content is priced.

IPod sales accounted for 29 percent of Apple's $5.4 billion in revenue last quarter, and the new models would hit store shelves in time for the key holiday shopping season.

Apple was also buoyed by a pair of reports, one from market research firm iSuppli saying the iPhone was the best-selling smartphone in the United States in July.