I picked up this Sonia Kashuk blending sponge from Target for $9.99 after reading about the Beauty Blender. I've been really pleased with this sponge so far because it makes application of my concealer and/or liquid foundation a cinch and helps to achieve a clean, even and natural look with less product.
The Beauty Blender retails for $19.95/ea or two for $25.95. I'm strongly considering trying it out, because it's larger and I've heard the quality is better, overall.
MAC is introducing their Pro Performance Sponge soon, for $18.
The one thing I always try to achieve when I do wear foundation is a natural even look. Each of these sponges will help to create a smoother and refined look; even skin tone without looking like you're wearing a mask. Another bonus is that they can be washed easily and used over and over again.
...photos from Target.com, BeautyBlender.com and MACCosmetics.com...