Mittens

I always recommend using wool for mittens, rather than a man-made fiber. It's amazing how much warmer wool mittens are, even when they're wet, your hands will stay nice and warm.

Bulky Mittens

Knit with super-bulky yarn, these are quick to knit and very warm. 
Yarn:  About 100 grams or 90 yards of super bulky yarn
Needles:  DPN's size S 11

Happy Mittens

I called these Happy Mittens just because the colors made me happy!
Yarn: 100 grams chunky yarn, such as Lamb's Pride Bulky, Lanaloft Bulky, or Harmony from Ironstone
Needles: DPN's size US 10

Ruffled Mittens

Cute ruffles wrap around the wrist of these mittens.  A matching hat is available as well. 
Yarn:  About 205 yards worsted weight yarn
Needles:  16" circular and DPN's size US 7