While I don't own as many as I'd like, I've always felt that graphic tees are closet staples that everyone should have. They instantly give you a cool girl vibe, are quite versatile, and are just plain fun.
Last winter I picked up a few graphic tees from work and loved how they added a little "oomph" to my blazer + jeans look. It's one of my favorite cold weather "uniforms", so now I'm on the hunt for more.