Ack sorry I meant more like wavy hair. :) Generally curling it doesn't work because it makes it too curly and not wavy.
Ah ok!
Right then. You can buy specific heat wavers now. They have like three small barrels all next to each other.
Other than that the easiest simplest way is to plait your hair in between five and ten plaits (obviously the smaller the plait the tighter the wave) when it is damp. Wait for it to dry, then undo them :D easy peasy.
You can also use a sea salt spray to help encourage that natural tousled wave look.
You can also, with flat irons, the same way you curl hair with them, create waves, just don't turn the iron on such an angle, put random bits throughout your hair, then use your fingers to separate and tousle to encourage the waves. If it curls too much, brush though it and it'll flatten the curls into waves.