I've found that my Irish Bog Oak pens have always been very popular. Possibly because of the age of the wood. At round about 5000 years old, the oak trees were alive and growing at the time that Stonehenge was being built! Or it may be that there are so many people around the world with Irish ancestry. Whatever the reason, I'll continue to make pens from this wood.
Building on from this idea, I recently found some pen parts with Celtic Knot inspired detailing. There's a ballpoint pen as well as a fountain pen. They're very high quality parts - solid brass - and the fountain pens feature a fantastic Schmidt nib. Both styles feature an emerald green glass cabochon on the top end. I've added a few to my shop to just to 'test the water' - some in Irish Bog Oak and some in an emerald green acrylic. They're not cheap, but they are some of the best quality pen components I have seen and they write fantastically - heavy, but beautifully balanced and oh so smooth!