I posted this ages ago on here. It's really easy and is the one I've used for charity knitting.It's from the Mission to Seamen charity website.
WOOLLEN HAT
Double knit wool.
Size 8 (4mm) Needles
2 oz of wool ( 50 gram ball)
Cast on 120 stitches.
Rib (2 plain 2 purl ) for 12 inches
Next Row – Knit 2 together to end of the row
Purl next row.
Repeat these two rows once more.
Knit 1 row.
Purl 1 row.
Pull thread through all stitches and sew up seam .
Stick a pom pom on top if you're feeling frivolous :)