This under eye concealer is my absolute fave right now. I got this in Primark back in July, while I was in Blackpool.. Yes, I did say Primark!
It cost about about £2/£3 and is awesomeness in a cute hot pink tube!
It is a lovely consistency, blends under the eyes really well and conceals excellently in my opinion. It reflects the light slightly, so hides any bad darkness, etc.
Here is a swatch (Sorry for the poor quality, It went a bit blurred) mine is in the shade 'light' and I don't know if they have other colours, but I would assume they do.
It comes in a tube with the little button that you press on the end which distributes the product into the brush on the end. You don't need much and it does the job! I tried to take a pic of one eye with and one without, and I can see the difference, can you? (I have not edited the lighting or anything on these, just cropped my zit ridden face out!)