The first product that comes to mind is Starbucks Coffee. In terms of product quality, their coffee is pretty awful and the random assortment of sugar drinks that happen to contain some coffee are even worse. It's true that the coffee is better than what you may get at your local diner but it not that much better, especially if you consider the price premium you pay to get a cup of SBUX.
From the marketing side, this has been their true genius. Their marketing and brand was built upon offering high quality coffee to the masses at a time when it was very difficult to get coffee outside of Folgers. To be fair, when they started their coffee was much better compared to what was available (and also using beans provided by Peet's in Berkeley).
For their many decades of existence, they grew organically without the aide of commercials or other traditional advertising methods.
What was their best advertisement? The coffee cup:
Starbucks' organic growth was largely filed by their customers walking around with a billboard in their hand that became a conversation starter and word of mouth referral generator for their growing business.
Starbucks jump started a national revolution in coffee that has spawned many local shops to provide much better quality and variety, which is where I choose to spend my $$$ these days :)