Hayrack window boxes are an English country staple. The addition of succulents here gives a modern rustic look and makes the whole business even more low maintenance. The coir liner holds water pretty well and can be easily replaced. Best of all, they won’t go out of style and they’re not hideously expensive. You can find some nice ones along with replacement liners here.
In this mix are Aloes for spiky forms, multiple echeveria varieties for fullness, aeoniums for height and some dwarf jade (also called elephant food or Portulacaria afra) spilling over the sides. Aeoniums are so versatile in size, color and form: some will grow long curving stems and branch, some will grow tall and lush, or you can break them off and replant them if you want to keep them short.