BB Ultra Fine Brush, angled stiff eyeliner brush or Sigma Eye Liner #E05. The stiff angle brush is wonderful for a winged liner. Sometimes I use two brushes to achieve the look I like. I bought this brush and I didn't really like it. I got it for around $7. I tried the angled/slanted Sonia Kaschuk brush but I just couldnt' get a straight thin line.
I like to use liquid liner too. I do well with felt tip liquid liners. L'Oreal Lineur Intense is really good. Also, Lancome's Artliner is fantastic. I want to try Stila's All Day liner along with the YSL liner which a MUA told me is the best.