Urban Decay Primer Potion. Fantastic product. I discovered this stuff thru Product Girl, and I'm really happy with it. It's basically just a nude cream you apply to your eyelid before you apply eyeshadow. It doesn't have any color, but it does help your eyeshadow stay where you put it. I bought a tube yesterday at Sephora and used it this morning underneath my eyeshadow. The picture above is my eye at around 1 in the morning, after about 15 hours (!) without reapplication. Notice, no creases! You'll have to take my word for it that there's the same amount of color on there now as there was this morning. I'm not sure what will happen when I apply a more liberal amount of shadow, but I'm optimistic. I'll let you know how it goes.
Because no one wants to reapply or worry about eyeshadow migration on their big day, I'd say this is a no brainer for $14.