Sam Nielson: Painter Brushes

Let me start this by saying that you will never get what you want out of your brushes in a digital art program (at least not with current technology).  You'll save yourself a lot of frustration if you accept this fact and learn to be happy with what is available.  Also, I'm not going to do a tutorial on Photoshop brushes because I haven't found anything I love yet (though CS5 might change my mind).  This has nothing to do with program superiority, just preference.
Here are some of my favorite brushes.  Most of these are are out-of-the-box brushes that come default with painter.  Before you try any of these out though, use the "Brush Tracking..." feature in Preferences (edit menu on PC, Apple icon on Mac I think).  Do a few strokes in the box typical of your pressure and speed and it will automatically calibrate Painter's settings to match your drawing style.  If you don't do this you may not like the "feel" of a lot of these brushes.

I'll start with the brushes I like to draw with:

The markers make ugly, soft, messy-looking drawings, but they're great for roughing things in, especially because of the way the marker strokes build on top of each other.
I use the round tip pens for inking, but I changed the Minimum Size of the brush to zero so I could have lots of scale variation.  If you make these brushes very big you lose a lot of control.
The charcoal is the closest I've found to pencil if I'm touching up a pencil drawing I scanned in.
The Liquid Ink looks great but is a bit hard to control, especially when the brush size is small.

Next up, my favorite cover brushes.  These brushes have little or no bleed, so it's easy to get fully saturated color:

"Custom 1" (settings below) is essentially an airbrush with the tip changed to something a little harder.  What's nice about this brush is you can use it for soft falloffs like you would with an airbrush, but if you want to get a heavy stroke with a fairly defined edge you just dig into the pressure a bit.  It sometimes has strange artifacts when using on layers of different types (like Gel).

The captured acrylic is my most used brush. I like the combination of the cover style of the brush with just a touch of bleed.  The only problem is it goes very slow if you make the brush very large, so use something else for your large strokes.
I don't use the square pastel often but it's a great brush if you want heavy texture in your strokes.  I often use the fade tool (Ctrl+Shift+F) to get lighter strokes since it's at full opacity.

My favorite "painterly" brushes have heavy blending at low pressure and apply color at high pressure:

I don't particularly like the Smeary Round but I included it because a lot of people I know do like it.  I never got very good at oil painting and it feels a lot like oil painting to me: everything just smears together.  I bet you could get great results with it if you were patient.
Custom 2 (settings below) is a very digital-looking painterly brush, but it gives such smooth yet slightly varied results that it can be really appealing when used correctly.  This is very similar to the brush Ryan Wood uses and until a couple years ago was one of my most-used brushes.

The Loaded Palette Knife is a lot of fun and gives a lot of texture and direction to your strokes.  The only change I made to this brush was setting the Angle of the brush to the "Bearing" of my pen.  This only works with Intuos pens.
Custom 3 (settings below) is about halfway between the palette knife and Custom 2.  I haven't used this one much lately but it's a great brush (I'd forgotten, but this tutorial reminded me) and I think I'll try to use it more often.

There are two other brushes I occasionally use:

The Glow Brush is great for glowing things.  Don't overuse it because it starts to look like cheap trickery pretty fast.
The Digital Watercolors are really nice for initially applying color over drawings.  I know Painter has some super-advanced watercolors now, but the old digital watercolors are faster and more approachable.  Just remember "Dry Digital Watercolor" in the Layers menu when you're ready to paint on top of them.

One final note:  Even the best brushes won't make you a better artist.  What brushes can do for you:
1-Speed up your process of applying and mixing color
2-Add visual interest with your brush strokes and layering of strokes
However, I've found that 1 and 2 don't usually go well together.  In fact, usually the more interesting a brush looks, the harder it is to paint with and vice-versa.  So adjust your expectations accordingly: if you prefer quick and easy-to-use brushes like me, don't be terribly surprised when your final results look like the digital airbrush job on some guy's truck.  Or, like me, you can just accept the cheapness of the results and be happy with the extra time you have because of it.  But if you really want things to look great, you need a lot of patience.