Sennheiser. I had a pair of reasonably expensive (~$250) headphones and the left ear went a week after my 2 year warranty expired. I knew it was basically just the cable (which was detachable), since it worked with a spare. But the official cable has an angled, custom fit and so it sits flush.
I filled in an online form, printed the pre-paid label, dropped it off at UPS. Within a week, no questions asked, a brand new pair showed up in the retail box (with another box, set of batteries, extension cables).
I've always found returns to manufacturers a huge pain in the ass, this was the first that wasn't.