To make it easier I have created a kit on Amazon, where you can pick and choose your supplies. You can also visit Dick Blick, Jerry's or Cheap Joes online
About color: whenever possible use professional quality transparent watercolors they have a higher pigment load, less filler and are ground finer giving you the best results.
Beginners: To keep the cost down student sets are fine try to use tubes not pans. Do not expect the same results with student sets as with the professional colors.
Important: For the color blending that I like use use Winsor & Newton for these colors, French Ultramarine Blue, Indigo, Burnt Sienna, Perm. Alizarin Crimson, Quinacridone Magenta.
Paper: try to use Arches 22x30 watercolor paper and tear it down to size, pad paper reacts differently and student brands will not give you the results you want.
Brushes: before investing into expensive brushes, or ones that don't work as well consider the ones I use. These are available in my workshops and on my website
Hake Brush: these have a tendency to loose hair, an easy fix is to squirt a little “Super glue liquid” along the edge of the handle and work it in.