Discontinued headphones that had great sonic characteristics, coupled with a lot of growth in the high-end headphone market.
The two that I owned were:
-- Joe Grado HP-1000 HP-1 (bought@ $700 , sold@ $1700)
-- AKG K-1000 (bought@ $750, sold@ $1250)
Both were amazing headphones. I especially loved the experience with the K-1000, but I never used them enough to justify them because I amped them with a pair of monoblock power amps which were normally connected to floorstanding speakers. The effort to change the cables coupled with the risk of burning out components if you wired something up loosely and one power amp was driven with no load lead me to rarely switch the floorstanders for the K-1000s.
Now I use a Denon D7000, which surprisingly works great unamped, but I'll be getting an amp in a few months probably.