Answered[ Edited ]
I personally love the Sephora Professional Platinum Powder Brush. I use it with my Nars Laguna Bronzer, and it does a wonderful job.
I use a brush like this one (http://sephora.com/browse/product.jhtml?id=P188217
I don't have a bronzer brush. I prefer using my soft and fluffy MAC powder brush instead. It just leave a very little hint of bronzer and gives me a very natural look. I know MAC is an expensive brand but their brushes are very soft.
Best of luck with your search
The very best bronzer brush that I've ever used (so far) is Bobbi Brown's Bronzer Brush which is a fantastic brush that helps diffuse and blend your bronzer, leaving just a hint of color on your skin. You can build the color easily without ever starting out with too much with this brush. You can find it at: http://sephora.com/browse/product.jhtml?id=P270576
It is a little pricey, but it is a good long-term investment that will last you for years.
I hope this helps you.
You should take a look at the bronzer brush from The Body Shop. It's so fluffy, yet dense. I love the softness of their brushes although I wish they would make the handles a bit longer.
Others I like:
The Sephora platinum powder brush #50 (the bristles on this one are a bit less splayed out giving you more control)
This one in particular will blend your bronzer in very well:
Hope this helps!!
I actually LOVE my clinique powder foundation brush because it is the perfect size and shape (it has a slightly tapered flat paddle like shape) and it is not dense at all, which is great for bronzer. I find that when I use dense brushes, it tends to deposit too much product, but this brush really just dusts my laguna bronzer over my face for a natural glow.