If it's Circulatory darkness (blue-ish purple present in the inner corner mostly) then I would recommend either the B. Kamins Therapeutic Eye Cream, or Peter Thomas Roth Power K. They both have an enormous amount of Vit. k which helps to repair capillary walls which leak blood in the first place, causing darkness to be visible.
If it's Hyperpigmentation, you want to look for Vit. c, and I would recommend the MD Skincare Lift and LIghten (a great choice if you're not sure which you have) or the Murad Essential C eye cream (with SPF15!) Keep in mind it will take about a month or more to see results from either of the mentioned creams. BE PATIENT!
I wanted to let you know about a product called Kinerase C8 Peptide Eye which is a powerful formula that banishes puffiness and dark circles under your eyes. It takes a few weeks to start seeing the full results, but Kinerase is a very, very good skincare brand and it does work. You can read about it at: http://sephora.com/browse/product.jhtml?id=P263004
I hope this helps you.
After years of caking on concealer, I discovered Hylexin. IT WORKS!!! Not cheap at $96 a tube, please know that this tube should last you around nine months, using it am and pm. Google it, that's how I was convinced. Good luck!