Contouring may be my favourite part of my makeup routine, but covering dark circles is easily the worst. There are all kinds of causes (anaemia, inherited darkness, late nights - see Lisa Eldridge's amazingly informative video here) but regardless they are a pain. There are a few things you can do to help reduce darkness from the inside (like getting more sleep, drinking more water and so on) but, for the most part, if you have dark circles you're probably going to end up down the camouflage route...which has its own problems.
Against purpley-blues, even your most trusty concealer can start looking a bit grey. On top of that I find most things crease on my undereyes and from time to time they can be quite dry. At night I use a hydrating eye cream, like Kiehl's Creamy Eye Treatment with Avocado, but in the morning something lighter, like Alpha H Complete Eye Complex, that won't cause concealer to slip and slide. To work around the worst of the creasing I try to avoid the deepest lines when applying concealer, which unfortunately tend to run parallel to the darkest areas, and I've also found a bit of priming helps. You could try your foundation or eyeshadow primer, but I've not found either to work particularly well.
I've had the most success with Clinique Even Better Eyes Dark Circle Corrector*, which only has a slight tint and some light reflection, but the oil free formula keeps any dry patches at bay and smoothes out the undereye area ready for concealer. The metal applicator is really soothing on the eye region too, helping puffiness and darkness. Giorgio Armani Maestro Eraser Dark Circle Concealer* is another option for undereye priming. If you've ever felt the Maestro foundation, this is the same silky formula which smoothes over the area and tends to help concealers stay in place, and crease-free, for longer. Although it's meant to be an eraser, I find it neutralises but doesn't brighten so works best underneath another concealer but it's a pricey option to just use as a base and I've found the packaging can leak a little as the formula is very liquid. On the budget side of things, Garnier Tinted Eye Roll on (not pictured) also works well as a 'primer', or alone on lazy days. The rollerball packaging is a bit messy, but a quick swipe helps to smooth over the area in preparation for something more heavy duty.
For correcting darkness, I tend to gravitate towards Origins Plantscription Anti-Aging Concealer*. It's very peachy (I have 02 Light/Medium), neutralising any blue tones, and the formula is silky and almost totally line resistant. Personally I'm not a huge fan of the Bobbi Brown corrector or creamy concealer as they both seem to migrate and crease quite badly, but I love their repackaged Tinted Eye Brightener when I'm in a hurry. It has just enough coverage to wipe out the worst discolouration but adds brightness too. I'm not quite in the YSL Touche Éclat hater camp, but I find it can just leave the undereyes looking a bit grey. Clinique Airbrush Concealer has more coverage, and a little more creaminess, to conceal and brighten. A cheaper alternative is Collection's Illuminating Touch Light Diffusing Concealer; it doesn't have quite as much coverage and leans a little more pinky-grey, but is still a nice option for adding light into the very darkest areas.
Finally, the concealer I've been loving which combines all three jobs (smoothes, corrects and brightens) is Perricone MD No Concealer Concealer*. It has an SPF35 mineral based sunscreen and vitamin C, which can prevent further darkening, and keeps my undereye area hydrated throughout the day. There are a couple of (one minor, one major) niggles however. Although it smoothes out the finer lines it can settle into deeper ones and it, frustratingly, only comes in one shade. What Perricone describe as 'one shade suitable for most skin' (oh puhhhlease, Mr. P) is a peachy-beige hue that is very similar to the Bobbi Brown Corrector in Light Peach. If you're around a MAC NC/NW20 to NC/NW30 you're covered, but lighter or darker tones may struggle.
Phewf. So there's my extensive round up of all things undereye camouflage. Feel free to share your favourites below.