I love Shu Uemura Synthetic Brush #10. If I only had one makeup brush, this would be it. I use it mainly as a concealer brush, but it also works wonderfully for eyeshadow (cream and powder), NARS Multiples, and for spot application of powder foundation. Retails for 35 dollars, and IMO it's worth it.
I really want to buy Natural Brush 18R Red, i was petting it in the store and it is so soft, and I love the color. It retails for 45 dollars.