Duo Fiber Crease Brush
I was first exposed to this brush with the MAC holiday 2011 mineralize brush sets for the Ice Parade collection. I have the SE sized brush, and loved it so much I bought the full sized.
This is made of goat (the black hairs) and synthetic (the white hairs) fibers, and is intended for use with their minerlized eyeshadows. I happen to like this for both standard and mineralized (baked) eyeshadows, as well as for using with shadows wet or dry. It works well for application as well as for blending.
The fibers are soft to the touch (not the softest, but soft), yet firm enough to not slop around when trying to blend. It has a domed shape, and even for my small eyes I find it a good size for application and blending without depositing or spreading color into too wide of an area on my eye.
This holds its shape well with regular usage and washings, and I really love this brush.
The MAC 286 Duo Fiber Tapered Blending Brush retails for $31 and can be purchased from MAC Cosmetics stores, counters, and from the MAC web site.