I use a brush like this one (http://sephora.com/browse/product.jhtml?id=P188217
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 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
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.
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.