Damon Darlin, reporting for The New York Times, pegs the iPod accessory market at $1 billion per year:
Not when making add-ons for the iPod is a $1 billion business. Does that sound like hyperbole? Consider this. Last year, Apple sold 32 million iPods, or one every second. But for every $3 spent on an iPod, at least $1 is spent on an accessory, estimates Steve Baker, an analyst for the NPD Group, a research firm. That works out to three or four additional purchases per iPod.