The hat I just made for my friends daughter used Moss Stitch for the hearts. I am now a huge fan of this stitch pattern, as it is super easy to do and gives beautiful results.
How to do moss stitch:
Cast on an even number of stitches.
Do your first row as follows: Knit 1, purl 1 across row.
For your second row, purl 1, knit 1 across the row.
Continue knitting, knitting your purls and purling your knits.
Keep repeating your rows until your work measures as long as you want it.
If you're binding off, make sure you bind off in pattern (purl the knits and knit the purls!)
NOTE: This is "British Moss Stitch", also known as seed stitch. "American Moss Stitch" is the same general idea, but the pattern is like this:
Row 1: K1 P1 across.
Row 2: K1 P1 across.
Row 3: P1 K1 across.
Row 4: P1 K1 across.
It ends up more spread out.