I was just going over photos and drafts when I realized I never talked about Hakuhodo K007 Eyeliner Brush, a classic thin eyeliner brush, that I've had for longer than I remember. Actually, I have two or three of them, since I use and test so many eyeliners, and this brush is also good for pinpoint concealing.
There are many good eyeliner brushes around (not to mention that you can also use art brushes for this purpose). Most of them look alike until you examine them closely and compare their performance side by side using various eyeliners, until you find which brush is ideal for each task. The uniqueness of Hakuhodo K007 is in the shortness of its hair (weasel. It grabs all the pigment you need in one go). It's closest to MAC 210, though the base of Hakuhodo K007 is thicker. The short bristles make the head non-floppy and easier to control, especially for beginners and those whose hand is less steady.
Bottom Line: an essential.
Hakuhodo K007 Eyeliner Brush ($15) is available from hakuhodousa.com. They offer worldwide shipping.