Urban Decay's Primer Potion in Original, and Lorac's Eyeshadow Primer. You may have herd the age old trick to apply concealer or foundation to your eyelid before applying your makeup, however, an eye primer works much better and prevents the makeup from creasing (where as concealer and foundation is thick and may crease your makeup).
One of the issues I have had with eye primers, however, are that they are sometimes tricky to apply. Often, I will get clumps of it stuck near the corner of my eye or on my lower lid.
So here is the tricks:
a) Begin by applying the primer to the outer corner of your eye and then smoothing it towards the inner corner. By the time it gets to the inner corner it will have smoothed out and will not clump.
b) You can apply the primer all over the lid (all the way up to the eye brow) or just above the crease (where most of your colour goes).
c) USE YOUR FINGER! I have found that using my finger is the fastest and easiest way to apply the cream. Do not use the wand the product may come with as it will apply too much product to the lid.
d) Only apply a SMALL amount to the lid, the more you put on, the more chance you have of clumping or creasing. The product should literally disappear into your eyelid and become invisible.
I hope this helps! Feel free to pick up some amazing samples of eye primers at your local MAC or Sephora stores!