I sometimes get a little OCD with my brushes. I want them all to match. I want to own every one in the set, even if I don't need it. And while I might like wasting my money on brushes I don't need, not everyone does.
So check it out.
If you have....
straight. You need a paddle brush. It's large area will help your hair to get smoother, faster.
volume. You need a round brush. They come in many different sizes, so depending on the look you want, choose the size accordingly.
short. You definitely need a Cricket Volumizer. Everyone needs one of these really. It does no wrong.
curly/kinky. You need a Denman. People with kinky curls swear by Denmans.
Obviously there are a ton of other brushes out there that do a ton of things. But this is just a general start to what could potentially be a large brush collection for you.
you've been warned.