PENS

G-PEN
(Zebra, Tachikawa, Nikko)
The most popular nib among manga artists, and as far as I know only produced in Japan. There IS a close imitation from Hunt listed below, but there's really no comparison. The G-Pen is the king of nibs; it can draw the thickest line of all the nibs but also as thin as a crow-quill. The pressure is set just right, it's easy to control the line's thickness and unlike a crow-quill or other "sharp" type nibs it glides easily on the paper. With a careful hand even small detailing, as usually done with a crow quill, can be done with the G-pen.
This type of pen is, of course, better suited to more "simple" style manga-ka; its highly variated line tends to screw up drawings with a lot of rendering/hatching and the like. I would say beg, borrow, or steal to get some of these, any brand is excellent.
Most prominent shonen manga-ka use G-Pens, among them Toriyama Akira and almost every artist with manga in Shonen Jump.

HUNT "Fine-Point 99"
This is the closest american nib to the g-pen- comprable line width/variation. It's harder to control, more likely to tear the paper, and a damn ugly shade of bronze. Give it a try if you can't get the real thing.

ROUND-, SPOON-, or KABURA PEN
(Zebra, Nikko, Tachikawa, Hunt)(Not to be confused with the maru pen, which means "round" in Japanese but actually refers to the "crow quill" type of pen.)
A strong, reliable, and easy-to-use pen which produces lines which are graceful, if a little lacking in impact. The largest type of nib, as its Japanese name("kabura"=turnip) suggests, it has a somewhat teardrop shape. The tip is not sharp like other nibs, it has a small spoon-like projection. As such it's kind of like an ultra-thin calligraphy pen; it breezes over the paper and almost never catches or blotches. Hunt actually produces a smaller version as well which is actually quite useful, Japanese versions are all the size of the larger Hunt nib yet have more balance and glide. Surprise.
The kabura produces the little line variation, so it's a good choice for those who press hard or who like boring linework. Most manga artists who use it have a bold outline style and then fill in thin-line details with a crow quill; this combo can look great if done well. It's also suited to artists who want to use a lot of tone and unnecesary effects(shojo-ish, ahem) as then the boring line is disguised. The kabura's line does, however go incredibly well with colored work; the flatness of the line makes the colors inside seem to "pop". Some manga-ka who use kabura pens are Masamune Shirow(Ghost In The Shell), Takada Yuzo(3x3 Eyes) and (Rurou ni Kenshin).

CROW-QUILL or MARU PEN
(same as Kabura)
The many varieties of these pens, so called because the part which connects to the pen stock is curved into a round tube like shape, generally produce the thinnest lines of all nibs. They make delicate and very beautiful lines, used mainly by shojo manga artists. Crow quills require a different type of pen stock than the other nibs, smaller and with a round hole at the tip.
The Hunt 102 is the "standard" crow quill, can make a razor thin line but is quite flexible. Not suitable for backgrounds as the line variation is too extreme. As this pen is quite flexible, it seems after it softens a bit it can be as dynamic as a G-pen..however, its weight is too light to "feel" and the holders for maru-type pens tend to be microscopic, so it depends on your hand size(perhaps).
The 104, "Stiff Hawk"(yes, ridiculous), is the best nib available in the US for backgrounds, drafting, and speed lines. Recognizable because the resevoir opening is totally round, it has almost zero line variation so goes well as contrast to more dynamically lined characters as their BG lines.
Hunt 108...what the HELL??!?? I think its an alien pen, its a brass color and has two huge, verrrry flexible phalanges on the tip(please, don't get excited....). The slightest pressure will make a fat, brushlike like line, and likely the pen will lose its resevoir and vomit the rest of the ink onto the paper as well. If anyone has a use for this weird creature e-mail me and let me know.
I have little experience with Japanese crow quills as I dont use the things! However, probably 85% of shojo manga is drawn with them.

SCHOOL PEN
(same)
The school pen is Japan's answer to the Hunt 104. It gives only slightly more thickness than a 104, with little variation when pressed, so it's even better for BGs, detailing, and speed lines.I also use it for word balloons, but only after its a little softened up. Glides better than a 104 as well, hahaaa!
The Hunt version is an entirely different beast- a piece of trash. A flexible and badly angled version of the Fine-Line 99, its is a sad excuse for a pen and almost guarantees you an ink blotch(and you wetting your pants). Stay away, far away.

to be added:Rotring Tech Pens, Micron Pigma, Procolor II