Never been disappointed at Trader Joe's or Nordstrom.
I'm a huge Costco fanboy but their policies are great rather than their customer service. Workers there have pissed me off plenty of times and they are not as friendly as Joe's or Nordstrom.
Came here to post pretty much this (though I haven't had any business with Nordstrom, so I can't comment).
Trader Joe's always has the most friendly people working there. Its actually pleasant shopping there, not to mention their prices are great (on some things, not so much on others (milk, for example, is way overpriced compared to Costco)), easy return policy, and fast lines.
I once asked why everyone who works there seems so happy, the guy said it was the pills they fed them each morning
Costco of course has an nice easy return policy too, but the employees don't care as much as Trader Joe's.
Amazon.com of course has great customer service. No questions asked returns, prompt service, etc.
Also had a very good experience with Coastal Contacts, some coating on my wife's eyeglasses got quite "foggy" from a few small scratches, and they sent out a replacement pair and we will send back the current ones when the new ones arrive. $180 glasses too, so I'm glad I didn't have to buy new ones. I wouldn't hesitate to buy from them again. Great service.
That's more or less the extent of my dealings with customer service (to any meaningful degree).