[Giant Fossil Penguin]

For me, GW brushes are perfectly good. As far as I'm aware (and there's the possibility it's changed) they are made of Sable, which is very desirable; they aren't too expensive, although doubtless if you know where to go you could get cheaper. They work well with the paint and come in a range of useful sizes. Plus, they're readily available.
Like I say, there will be other, better brushes out there, but GW ones will be easily good enough; hell, 'Eavy Metal use them, so they must be somewhat useful!

GFP