Fake Z-warriors
These illusions of Gohan, Piccolo, and Gotenk appear only in the anime to Goku and Vegeta while in Buu's stomache. Since they weren't real, Goku and Vegeta beat them easily but they didn't feel pain and they couldn't be defeated. They eventually just disappear.
Firefighter
This firefighter of Satan City was the first normal human to give his energy to Goku's Genki Dama. He just wanted to see what would happen if he raised his arms like Vegeta was pleading.
Followers of Lude
These are all the people turned into dolls by Doll-Tucky. They are freed when Goku and Pan kill the Lude Monster.
Frieza/Furiza
Frieza is one of the most important villians in DBZ. His orders cause the destruction of almost the entire saiya-jin race, thier planet, and many other worlds and peoples. He traveles to Namek to search for the draon balls. He has many forms to hide his true power. His first is short and looks like Mega Man. The second is taller, like King Cold. The third resembles the queen from Aliens. The last is shorter and designed for fighting. When he is defeated by super saiya-jin Goku, he is rebuilt into Friezabot and traveles to Earth for revenge. He is then chopped into peices and burnt to dust by Future Trunks. He returns in movie 12 but is quickly killed by The Great Saiyaman Gohan in one munch.
Frieza's Scouts
There are many different groups of scouts. One group is met by Gohan and Krillin and misjudge thier strength and are beaten. Another group is beaten by Future Trunks when Friezabot came to Earth.
Future Bulma/Mirai No Bulma
Future Bulma is very seldom seen but plays an important role. Without her there would be no time machine so Goku would not have had the medicine to save himself and the others wouldn't have gotten ready for the androids. Cell also couldn't have come back to the present.
Future Gohan/Mirai No Gohan
Gohan is the only survivor from the bttle with the androids. He spends his entire life training to become as strong as his dad was to defeat the android. Gohan looses one of his arms in one of his battles with 17 and 18. When the androids attack the West Capital, Gohan goes to face them but knocks out Trunks so that if he died there would be someone left to face them. He put up a good fight but was killed in the end. His death cuased Trunks to transform to super saiya-jin for the first time.
Future Trunks/Mirai No Trunks
Trunks is my favorite character and a very important one. He comes back form the future to tell the Z-warriors of the impending danger of the androids. When he arrives, he makes short work of King Cold and Frieza. He returns to help with the fight against the androids. After training in the Room of Spirit and Time, he was the strongest of the Z-warriors. When Cell returns from his own self-destruction, he mercilessly kills Trunks without warning. He is brought back to life through the dragon balls and then returns to his own time. He easily kills the androids (which are weaker in his time) and Cell. He always carried a sword given to him by Tapion until it was broken by Andriod 18.