A day doesn't go by that I don't check in with one of my trusty resources. And if I know I'm going to be on a long car ride (I'm not driving of course) or stuck in a doctor's office waiting, I'll grab one to get some extra studying in.
Having said all that, the following is my current top go to books for information. Several of the artists have developed brush strokes that, although are beautiful and to be admired, are not of my style. Still, much can be gained by studying their various techniques, including color mixing, paint application and breaking down the process as a whole.