Pricier: Bobbi Brown Blush.
Cheaper: SpaResource (at Wal Mart) Blush Brush. The EcoTools one is okay, but they seem to have a real quality control - the two I own are two completely different shapes...
I really like the Sonia Kashuk Small Duo Fibre Multipurpose Brush. It's supposed to be a dupe for the MAC 186 (not sure if that's the right #). This brush gives me more control on how much color I pick up. Plus, it's inexpensive and doesn't shed like my MAC did.
I've been using it for 4 years and it's still going strong. I love that I can use the dome shaped head of the brush, or the flatter side depending on the type of application I want and it's very controlled since the bristles don't splay out.