You can use pretty much any headphones with a 3.5mm plug. The connector is a bit stiff, so be careful with any plugs that have a sleeve, but other than that, I haven't had any issues.
The "Sonas" Nook earbuds, which were designed by Jays of Sweden, are no longer manufactured.
The current Nook branded earbuds and headphones "Nook Audio" are designed by Bose. These created a splash when they first appeared and showed up as Nook Audio IE250 and OE250 with no picture and no description a few moths ago (eople assumed a new MP3 player or audio service).
I cannot currently find these on the site, however B&N has a bad habit of completeley removing listings that are sold out.
Long story short (too late) you can use any phones with an 1/8 inch / 3.55mm headphone jack.
Apparently B&N has discontinued them. However....I can get them from Amazon....same model and for about $5-5 dollars cheaper. Rah,... yeah...Amazon. Seems strange.