This fine tip brush pen is the perfect all around pen for lettering. The fiber tip is flexible and sturdy enough to manage my heavy hand without complaining (not that pens actually CAN complain, but you know what I mean). They come in 12 different colors, but are sold separately, so you can mix and match all you want.

The ink is water soluble, which means that you can also dip it in watercolor, for instance, to make a gradient effect in your letters. The line width can vary from approximately 0.5 to 2.0 mm, depending on the amount of pressure.