An eyebrow pencil such as this one lets you experiment and play with the shape of your eyebrows and get them just right. This product is waterproof, which is very handy during summer.
From Selfridges
Bobbi Brown Blond Perfectly Defined Long-Wear Brow Pencil
Lookfantastic
Bobbi Brown Perfectly Defined Long-Wear Brow Pencil (Various Shades) - Blonde