I use Bobbi Browns concealer brush & i quite like that! LMAO because you asked for rec's and you'll never be able to make up your mind now with all the different brands mentioned! Maybe you should check out the review center to see if one in partuclar gets better reviews than others!
I use the MAC brush too. It doesn't tug on my skin and makes it easy to blend out the edges. I often wear mineral makeup, rather than liquid foundation, in the summer and easy blending makes a huge difference in how long it takes to make my face up.
Now, if only I could find a concealer that would last through my 10 hour work days!
I actually use a lip brush (L'Oreal to be precise); it is much smaller than any of the wide, flat concealor brushes I saw in the drugstores... I never saw one like the one Trisha posted in my price range, but hers looks fun too
I just use it under my eyes, and I like it because it allows me to get the concealor right up to the lashline without poking my eyeball with my fingernails (which usually happens when I don't use a brush!). I still finish blending with my fingertips to smooth things out, though.