Great closeups, Rob!
To answer your question, here's a quick summary (I had a longer one all typed out when the power decided to go out here on a nice, sunny day. Don't you hate that!):
1. Dip pens. Cheap, quick, somewhat messy for slobs like me. Offer a variety of lines widths. Not very portable.
2. Prefilled drawing pens. Cheap, portable, come in some colors. Some people like a finer nib than the smallest, but a good choice. Usually archival. Good choice to start with.
3. Technical pens. Nonvariable width of line, but infinite variety of sizes and colors, since you fill it yourself. You can mix colors, dilute strengths, whatever you want. High maintenance, particulary in smallest nib sizes. More expensive. If you go this route, read up on maintenance.
4. Cheap bic pen - the kind you find on the floor.
See work by maori boy, dolors, and drwells.
Hope that helps!