The Canadian Ciele Athletics makes fantastic running caps. Just make sure you buy the right size. 

Ciele Athletics Size Chart

You measure your head circumference and that corresponds to the size of the cap.

ALZCap

The ALZCap is a slightly smaller model. It comes in a standard size of 56.5 centimeters, but is adjustable. This cap with a head size of 56.5 CM fits a head circumference of 53.5 CM to 59.5 CM.

GOCap

The GOCap is the standard model, where Ciele originally started with. It comes in a standard size of 58 centimeters, but is slightly more adjustable. This cap with a head size of 58 CM fits a head circumference of 55 CM to 63 CM.