Hats are quick, sometimes easy, and fun to knit. I think of all the hats I've made over time, I have only followed one or two patterns. They are easy to modify and make your own. Quite often I will start with a pattern that interests me and then will modify the colors, patterns, sizes and overall shape. Once you understand the basics, such as the ribbed or rolled bottom, knit stitches and how to decrease, you can create something totally unique! They're also a good project to use up some of your left over skeins.
Mittens are also fun, I prefer to use double pointed needles rather than 2 needle patterns... anything to eliminate a seam! They knit up fast, especially if you use nice, chunky wool.