The Pigma brush pens were the first brush pens I tried. The black never seemed to hold enough ink for my needs, but I used it a lot! The best way to use it is with slow strokes. They fill in and blend more evenly than traditional markers and you have the added benefit of being able to make different thickness strokes.
If you use it fast, you can almost achieve a dry brushing effect. The colors allow for the same beautiful feel of brushes and the colors are bright and crisp! I feel they are a good midrange quality and a pretty good bang for the buck.
If you want a little more ink in the brush, you can get it with Sharpie. The color range is nice and they tend to be cheaper.
You can also start your exploration with Sargent: The least expensive, but still reasonable quality brush-tip set.
OR, you can dive in with both feet and get the near infallible Prismacolor pro set. The range of hues and tones combined with the fluidity of the ink are awesome for illustration and Manga work. These seem to be a favorite among graphic designers. Well, at least the ones I know.