One of the unintended consequences of the success of the iPhone is that it has rendered the classic iPod and its diminutive sisters — the nano and the shuffle — nearly irrelevant. What do you need a second MP3 player for if you’ve already got a few hundred tunes in your pocket?

Apple (AAPL) was able to goose sales for a while last spring by sharply cutting prices on the iPod nano, but the tide is drifting away from the company’s iconic product — which once accounted for nearly 50% of its annual revenue. By last Christmas, sales of iPods, which enjoyed triple-digit growth as recently as 2006, had nearly flattened out. If something isn’t done, they could soon be headed south.

Enter Steve Jobs, who is expected to appear in person at the Yerba Buena Center for the Performing Arts in San Francisco next Tuesday for a special media event entitled “Let’s Rock.” Jobs has made an annual ritual of introducing new iPods in September — giving the company plenty of time to ramp up for holiday sales. In 2005 the star of the show was the original iPod nano. Last year it was th