My favourite brush is actually a dog brush! It's a double sided brush - one is about the same as a stiff body brush, and the other has wider, metal bristles (I'm sure there's a name for it but I can't think of it) that works great for manes and tails. That way I can take one brush and it does the work of several. (This isn't the same brand, but this is what it looks like: Amazon
.com: Safari Pin & Bristle Medium Brush..."> Amazon.com: Safari Pin & Bristle Medium Brush...
(Of course there's the other basics in there too - hoof pick, clippers, rags, detangling spray, etc)