I recently purchased a pair of Phiaton MS 300 headphones based on a Head-Fi recommendation (which, incidentally, sound great until the plastic breaks next to the cup, both on the original and the replacement pair!). Upon hearing them, my dad, who listens to music constantly, decided to replace his $5 headphones from the early 90's with a new pair of high quality headphones, leaving me to figure out which pair is best.
He listens mostly to acoustic/folk music, with a little bit of classic rock thrown in. He doesn't care about base overly much, although it shouldn't be lacking completely; regardless, a pair with strong mids and highs would be best. He's looking for very comfortable, circumaural headphones (he'll probably be wearing them for 8 hour stretches at a time or longer). If his last pair are any judge, he'll probably have these headphones for another 20 years, so build quality and durability is important. :P
Lastly, as I mentioned in the title, his budget is from $80-$100. I tried to convinced him to go a bit higher and spring for some ATH M50's, which are recommended everywhere here and I have actually heard for myself, but he doesn't want to go higher than a hundred. Can ya help me out? :)