A US cup is about 237 ml. Rougher equivalents are 240 ml and 250 ml, where the latter fits nicely with a US pint of 500 ml and a pound of 500 g.
A Japanese rice cup is 180 ml. A measuring cup of this size is sometimes included with rice cookers.
A teacup, often seen as a unit of measurement in Indian recipes, is about 190 ml, or ⅔ of an imperial (UK) cup.