Vegitto

When Goku and Vegita fuse, they become Vegitto (Vegita+Kakarott=Vegitto), the most powerful character in the DBZ world. (I've also seen his name as Gogita, but this is from a DBZ movie and not the original manga.) Like Gotenks, Vegitto has a huge ego.

Pan

Pan is Gohan and Beedel's daughter. She first appears in the last two installments of the manga before it ended. Needless to say, we never get to learn a lot about her before the series ends. She looks just like Beedel did at 16, just a lot smaller. She's pretty tough in a fight for her age and size, and certainly has the potential to become fairly strong.

Bra

Bra is Trunks' little sister. She looks like a carbon copy of Bulma when we first see her way back in DB book #1, only much smaller. Like Pan, she only appears in the last two installments of the manga and only speaks a single line in those installments so it's tough to say much about her.

Uub

Uub is a polite little kid with a mohawk, another character who doesn't appear until the very end of the series. Actually, he is the reincarnation of Original Buu. (Uub=Buu backwards) He is very powerful for a human his age. At the end of the series, Uub goes back to his home town with Goku, who is going to train him.

The "Bad Guys"

Pilaf, Shuu, and Mai

These are the first set of villains presented in the DB world (on TV, that is; in the manga the Usagi-dan came first) Pilaf is a small blue imp determined to rule the world. Shuu and Mai are his underlings. Shuu is an anthropomorphic animal in a ninja costume, (what IS he, anyway? A fox?) and Mai is a woman with long black hair. None of them pose any direct physical danger to the good guys, (although they once imprisoned them in a death trap and later released the old Piccolo.) and are very comic characters in general.

The Usagi-Dan

The Usagi-Dan is a group of people who run around in rabbit ears and terrorize the peace loving populace. Their oyabun is a large rabbit with sunglasses named Toninjinka, whose touch can turn you into a carrot. (Oyabun is a leader of the Yakuza, the Japanese mafia) In one episode of the series (2 manga installments) they stood in Goku's way, turning Bulma into a carrot, but were eventually stopped with Yamucha's help. Goku then took them to the moon using his Nyoibo, so I guess they technically died when Mutenroshi blew up the moon :)

The Red Ribbon Army

The Red Ribbon Army is another populace-terrorizing organization, set on finding the Dragon Balls so that the leader can make himself taller. They played a major part in the first series, as Goku singlehandedly opposed them. The important members of the Red Ribbon are:

Red Sosui: The leader of the Red Ribbon army, Red Sosui is a very short man who is very hung up on his height. He secretly wants the Dragon Balls to become taller. He despises failure and executes any of his soldiers who fails on the spot.

Black Hosa: While Red is the leader of the Army, the true coordinator of everything is Black. Black is Red's top advisor and the trainer of the army forces. He is really idealistic and wants to see the Red Ribbon Army conquer the world.

Silver Taisa: Silver Taisa is one of the officers of the Red Ribbon in charge of searching for the Dragon Balls. He is fairly strong, but is no match for Goku.

White Shogun: The head of Muscle Tower, White Shogun terrorizes the north section of the world, focusing his efforts on Jingle Village, a nearby town.

Metallic Gunso: A robotic man who mans one of the floors of Muscle tower. He is quite tough and can take a lot of
punishment.

Murasaki Socho: A ninja who is very fast and has lots of tricks up his sleeve. He serves as one of the top commandants of Muscle Tower, second only to White.

Buyon: Well, not a real member of the Red Ribbon Army, Buyon is a rubber-like monster who lives in Muscle tower.

Blue Shogun: One of the strongest members of the Red Ribbon Army, Blue Shogun can fight and has psychic ability to back it up. Of all the officers of the Red Ribbon army, he was a threat for the longest period of time.

Violet Taisa: We never get to see much of this character. She's a woman with short hair. She appears in one panel, so there's not much to say about her.

Yellow Taisa: Yellow is an anthropomorphic tiger. He attempted an assault on Seichi Karin but was foiled by Goku and Bora.

Copper Shogun: We never get to see this character, he's only mentioned, but since he's a Shogun, he has to be important in some way to the Army.

Goku almost singlehandedly defeats the Red Ribbon Army. One of the scientists of the Army, Doctor Gero, survived, however and caused lots of problems for Goku and company during DBZ.