This is another hats post (I really do love the hats pattern--it is so flexible, and easy).
This one is done with two strands of worsted weight yarn, on 8mm needles. Cast on 30 sts. Create wedges by knitting to 22 sts, then turning around and knitting back; knit to 23 sts, and knit back, and so on until all the sts are used up. Continue until 5 wedges have been made--and then check your size. You may need another full wedge, you may not. If you don't, then cast off and sew together.
My niece walked in while my nephew was trying one on, and said: Awesome hat--where did you get it, and can I have one? (all in one breath, no pause!).
These are fast, and easy, and really good stash reducers.