HD 558

Sennheiser HD 558 and Rihanna. The clarity and impactful bass was just off the charts for my first real solid open headphones.

Almost any Sennheiser headset. I have the original PC 360 G4ME, which are modeled after the HD558, and it's genuinely the most comfortable headset I've ever had. The velour pads are incredibly soft, and the clamp strength is just right. Even at 8+ hours of use I don't even register they're on my head. I would imagine the actual HD 558 or similar ones like the HD 560, 598, 599, 6xx etc are all just as comfortable. I also have a Beyerdynamic DT770, and while they're comfortable they're not *as* comfortable as the Sennheisers. Closed back headphones tend to feel inherently a bit more clampy and fatiguing. The DT990 are open back though and probably on par with Sennheiser sets.

When i was a teenager i went from rocking Bose Quietcomforts to Sennheiser 558s, which are open-back headphones. I found it ironic when people would try out my Sennheisers and say that they had good noise cancellation when it’s the other way around, they are open to the outside and are intended for the studio. Though they worked way better as casual headphones than the Bose.

Similarly went with a 558 almost fifteen years ago now. Kinda miss them still. 

I consider discontinued HD330 (later HD465 I think) as the best on-ears I've heard, but they are pain to refurbish - no direct replacement for earpads or rubber/silicone headband strap (straps can still be in good condition though). There is a higher model HD340 / HD475 which I haven't tried, nor anything Grado. I consider the above to be better than 60Ohm Koss (not a comparison really), or the very popular HD480 Classic II, or some more current lower-mid level over-ears like HD559, but not as good as say HD555/558/579. I might pick them over HD599 though, just because I don't like the bloated tonality of HD599. So all in all, it is still not the level of hundreds of dollars, but very usable.