The Girls of Shonen Manga

The Tomboy
Tough and independent, with a short fuse and a tendency to beat the stuffing out of the hero with very little provocation. Often, the Tomboy claims to have no interest in the hero, even when her attraction to him is painfully obvious. She's usually the primary love interest, and if the hero is forced to choose a mate by the end of the series he will almost certainly pick her. Their inevitable union does nothing to solve the central mysteries of the Tomboy: Why would a spirited, outgoing girl be attracted to a boy with the personality of a wet dishrag? And why would a boy—any boy—be attracted to a girl who keeps punching him into orbit?
Signature Gags: She can't cook! She thinks the hero's a pervert!
Signature Angst Moments: Admitting she really does kind of like the hero; admitting she's Not Really That Strong.

The Shy Girl
Occasionally, the hero's primary love interest is not a Tomboy, but a shy, withdrawn girl who can't work up the nerve to confess her love. Often, she's a childhood friend who's long admired the hero from afar. The Shy Girl is a relatively rare type, mainly because she's boring. If she shows up, expect lots of tears and elaborate bento lunches, and probably a tie-in dating sim game.
Signature Gags: None.
Signature Angst Moments: All.

The Priss
A prim and proper young lady from a good family. In fantasy manga, she may be a princess or priestess; in more down-to-earth settings, she's in line to inherit a temple, a dojo, or just an uber-respectable name. She may be wealthy, although it's not a requirement. She often gets a lot of face time, especially if she has an elaborate backstory to explain her family situation. But she rarely comes first in the hero's heart, probably because she'd obviously be a drag in the sack. Prisses and Tomboys are natural enemies, so it's common to spot this type at the center of a catfight.
Signature Gag: She's such a snob!
Signature Angst Moments: Flashing back to her painfully traditional upbringing; showing a chink in her oh-so-proper emotional armor.

The Ditz
A childlike woman (often with a very adult body) who leaps all over the hero like a puppy and routinely forgets key articles of clothing. Often the Ditz is a foreigner, to explain her ignorance of concepts like "modesty" and "personal space." Other times, she's just stupid. The Ditz is seldom a serious contender for the hero, with occasional exceptions like Ranma 1/2, where Shampoo (an unusually aggressive Ditz) puts up a good fight. Her primary function is to provide random, unmotivated fanservice, and therefore she is essential to harem manga
Signature Gags: Oops, she forgot her clothes! Wow, she's clumsy!
Signature Angst Moment: Gazing at the hero with huge, moist eyes, usually after screwing up yet again.

The Little Girl
What fantasy for socially immature nerds would be complete without a prepubescent schoolgirl? The Little Girl is seldom presented as a serious love interest, except in Tenchi Muyo!, which constantly beats the reader over the head with the notion that nine-year-old Sasami is the perfect woman. But the Little Girl usually has a big crush on the hero, and she participates in fanservice along with the rest of the female cast. For reasons that may only make sense in the Japanese male mind, she often does lots of cooking and cleaning. Her other key function is to generate merchandise.
Signature Gag: Look how cute she is doing that cute thing!
Signature Angst Moment: Crying until the hero feels bad.

The Experienced Older Woman
A grown woman who hangs around the outskirts of the teenage cast, smoking, drinking, and offering to corrupt the hero. The EOW presents a serious threat to the balance of the harem because she's perfectly happy to have casual sex, which would destroy all that delicious romantic tension. Therefore, she's usually restricted to minor roles, or else bizarre permutations like Tenchi Muyo!'s Washu, an Older Woman who's physically twelve years old. The template for the type is Akemi, Maison Ikkoku's perpetually drunken bar hostess, although heroine Kyoko is technically an EOW herself.
Signature Gags: Drunk again! Propositioning the hero!
Signature Angst Moment: Realizing she's getting too old for this crap.

The Mascot
Similar to the Little Girl, with the same basic function (merchandising), but even less connection to what an adult human being might recognize as a potential mate. The Mascot is small, cute, and nonhuman. She's likely to have a limited vocabulary, and even more likely to spend most of her time in the backgrounds of scenes, doing housework. She's not remotely plausible as a love interest, but once she appears she'll become one of the most popular characters, obsessed over by preteen girls and middle-aged men alike.
Signature Gags: Aww! How cute!
Signature Angst Moment: Realizing she has no actual purpose in the story.