For me, it's all about the lower lash smudge. I spend quite a bit of time blending darker shades into the crease of my eye and making it look perfect but the look is never complete without the lower lash smudge.
It suits my eye shape so I always take my shadow under the eye, but every now and again I really go for it and do a bit of a Mary-Kate Olsen. I focus the colour on the outer corner of the eye and use less toward the inner tear duct area. Eyeshadows I've found that work really well for this are MAC Cork, Soba, Texture and Charcoal Brown. Buck from the Urban Decay Naked palette also works well, but you can use any kind of matte brown shade really.
Take a pencil brush and go wild, or if you're feeling really adventurous use a soft eyeliner and smudge it out. The Clinique Quick Liners are great and come with a smudger on one end, I also like the Rimmel Scandal Eyes liner in Bronze.
So next time you do your eyeshadow, try take the colour just that little bit lower and see how you like it!