Here are all the deaths that have happened in the series of Dragonball Z, and some from Dragonball. Obviously we can only write as many deaths as we have witnessed, so this section will grow within time. In some cases, people haven't died, but have been sealed away, etc. I count this as something as close to death as you will get, and have added it. I have stated what the situation is with these cases though.
The deaths from Future Trunks' alternate timeline or in yellow. The characters who only died in movies have a star next to them.

Good Guys

Android #16
1. Killed by Cell. Had head thrown onto platform so he could speak to Gohan, and Cell stamped on his head, crushing his skull.

Bardock
1. Killed by Frieza. He tried to kill the evil one once and for all, but wasn't anywhere near strong enough.

Chao-zu
1. Killed by Piccolo Daimao in Dragonball.
2. Self-destructed himself while attached to Nappa, in an attempt to destroy him. He failed, and died for nothing.
3. Died by the hand of the androids in Future Trunks' alternate timeline.

Dende
1. Killed by Frieza. He was discovered to be a healer, and Frieza killed him with a one-finger blast to eliminate the problem.

Gohan
1. Future Gohan was killed by the Androids after fighting with one arm, and eventually being rained down upon with energy beams, killing him outright.

Goku
1. Died during the fight against his brother Raditz. He allied with his former enemy Piccolo, and held Raditz in place while the Namek shot a beam right through both his and his brother’s chest2. Future Goku dies of a heart virus. He picked it up during his trip to Yardrat, and no cure had been invented to date. Note: This is future Goku, from the alternate timeline that Mirai Trunks is from.
3. Killed after he teleports Cell and himself to “Another Dimension” in order to save the world from Cell exploding. He lands on King Kai’s planet, just before Cell can finish his self-destruct attack. 
Guru
1. Died of a broken heart. Whilst on Namek, after all of his people had been murdered, he was so sad that he passed away.
2. Died of natural caused. He was wished back alive, and passed on whilst on Earth, with it being his time to die.
 
Kami
1. Killed when Piccolo sacrifices his life to save Gohan (The two Nameks are of one soul)
2. Killed when Piccolo dies in future Trunks' alternate timeline.
 
Krillen
1. Killed during a tenkaichi budokia competition. One of Piccolo’s henchmen ruthlessly killed him.
2. Killed by Frieza. He was hoisted in the air by some sort of psychic attack, then was exploded in mid-air. This is what triggered Goku’s transformation to super Saiyan.3. Killed in the alternate timeline by the evil androids.
 
Master Roshi
1. Killed by Piccolo Daimao in Dragonball
 
Piccolo
1. Killed by Nappa, whilst sacrificing his life for Gohan. He dived in the way of the Saiyan’s beam. 2. Future Piccolo was killed in Trunks’ alternate timeline by the androids. 
Tapion*
1. Sealed into a small music box, to keep out a monster. This, for him, was death, as it sealed his soul away. He was later released though.
 
Tien
1. Killed while fighting Nappa. He used such powerful attacks that he died of exhaustion.  
2. Killed by androids in Future Trunks' alternate timeline.
 
Toma*
1. Killed by either Dodoria or another one of Frieza's henchmen. Conquering planet Meet for Frieza, and was betrayed by soldiers with orders from the evil one to exterminate Saiyans, with them killing him.
 
Trunks
1. Killed by Cell. Cell pointed his finger out, and shot Trunks right in the chest. Vegeta went mad at his sons death. 

Vegeta
1. Killed by Frieza after trying to tell Goku some important information, he had a one-finger cutting beam shot right through his chest. It happened twice, with the second one succeeding in killing him.
2. Future Vegeta died in Trunks’ alternate timeline by the hands of #17. 
Yajirobe
1. Was killed by the androids in Future Trunks’ alternate timeline.  
Yamcha
1. Killed by a Saibaman. He defeated him in battle, but the saibamen cowardly jumped back on him when his back was turned, and self destructed, killing them both.
2. Eaten by Majin Buu after being turned into chocolate.
3. Killed in the alternate timeline by the androids.

Bad Guys

Android #17
1. Absorbed by Cell, and then killed during the self-destruct attack because he was stuck inside the monster and couldn't escape.
2. Fused with another Android #17 in GT. Taken out by the Z soldiers though.
3. Killed by Trunks in the alternate timeline. Trunks returned and easily defeated the android.
 
Android #18
1. Killed by Trunks in the alternate timeline. Trunks parried a blitz of energy balls from her, then blasted her in the face, killing the android outright.
 
Android #19
1. Killed by Vegeta. Vegeta saved Goku from certain death, then went on to kill this overweight android with a Big Bang attack.
 
Android #20 (Dr Gero)
1. Killed by his creations - Androids #18 and #17 in the alternate timeline from whence Mirai Trunks came from.
2. Killed by #17. His head is crushed by his own creation.
 
Brolli*
1. Killed by a triple KameHameHa from Goten, Gohan, and (In either his spirit or physical form, it was never revealed) Goku.
2. Cloned, then killed by Goten and Trunks, with them using an arsenal of attacks, including powerful KameHameHa's, exploiting his weaknesses.
 
Buu
1. Killed by Goku
 
Cell
1. Killed when he and Gohan matched KameHameHa’s. Gohan only managed a one-handed one, because the other was out of its socket. It was too powerful for Cell though, and overwhelmed him. 
Cui
1. Killed by Vegeta. Underestimated the Saiyans power, and was annihilated.  

Dodoria
1. Killed by Vegeta. He was beaten up, then supposedly shown mercy, but Vegeta blasted him as he flew off into the distance.

Dr Willow*
1. Body destroyed by avalanche. Remainder of him killed by a Goku spirit bomb.

Dr Kochen*
1. Killed by Dr Willow. He turned out to be a robot assistant, and plummeted to his death when willow opened up a crack in the floor by stomping on the ground, inadvertently killing Kochen.
 
Frieza
1. Killed by Trunks, who had come back from the future, just in time to stop Frieza and his father King Cold from destroying the Earth in revenge on Goku. He cut the evil being into many tiny pieces, then fried him.
2. Killed by Gohan (movie 12). He lunged forward, and buried his fist in Frieza’s gut, then blasted a hole through his stomach.3. Future Frieza was killed by Goku. This happened in the alternate timeline that Trunks lived in.

Garlic Jr
1. Whilst not strictly killed, he was plunged into the Dead Zone, which was an alternative to death so-to-speak, by Gohan. This was in movie 1
2. Once again, hit into the deadzone by Gohan. This was for good though. This was from the series.
 
Ginyu Force
1. Jeice-Killed by Vegeta during the Frieza Saga. The fought for a while, then Vegeta finished him off with a Big Bang attack to the face.
2. Burter-Killed by Vegeta during the Frieza Saga. Goku beat him up, then Vegeta finished him off.
3. Guldo-Killed by Vegeta, just as he was about to destroy both Gohan and Krillen. Vegeta dashed in and released a powerful punch to his chest, followed by a beam that killed the Ginyu Force member.
4. Racoome-Killed by Vegeta during the Frieza Saga. Goku defeated him, then Vegeta finished him off.
5. Captain Ginyu-Technically killed by Goku when Captain Ginyu tried to change bodies with Vegeta, Goku threw a frog in the way at the last second. Captain Ginyu would then live the rest of his life as a frog from then on.

Janemba
1. Forced to transform by SSJ3 Goku. Killed in its most powerful state by Gogeta, with an energy beam right through it's stomach.
 
King Cold
1. Killed by Trunks. Came to Earth to cause suffering, but Trunks stopped him, blasted him in the stomach, then in the face, killing him in a painful manner.
2. Killed by Goku. This happened when he came to Earth in Future Trunks' alternate timeline.
 
King Vegeta
1. Killed by Frieza. He went in to try to kill the evil tyrant, but was easily defeated.
 
Kula*
1. He was pretty much killed by Goku when hit with a KameHameHa into the Sun. Everything died apart from his brain and a fragment of his skin. Whilst not strictly dead, as close as you could become.
2. Returned as cyborg Kula, only to be killed once again by Goku, who used a powerful energy ball (May have been a spirit bomb, I couldn't tell in my fansub).
 
Lord Slug*
1. Killed by Goku. He was distracted by Gohan's whistling, then finished off by the powerful Saiyan Goku.
 
Nappa
1. Killed by his own ally Vegeta after he lost the battle to Goku. Vegeta thought that he was a weakling, so he decided to dispose of him by throwing him into the air, and blasting him with a beam of awesome power.
2. Killed by Vegeta again in DBGT
 
Nappa's Saibamen
1. One self destructed to kill Yamcha. After being defeated in battle, it cowardly attached itself to Yamcha, and blew them both up.
2. Three Were killed by Krillen. He released an awesome blast that separated into many different energy balls, and rained down on them, with one getting away.
3. The one that escaped Krillen's blast was killed by Piccolo. It went to attack Gohan, but the Namek stepped in, grabbed its arm, threw it in the air, then it with a breath blast.
 
Piccolo Daimao
1. Killed by Goku. When fighting the Saiyan, he was attempting to kill him, but was defeated from Goku punching right through his chest.

Piccolo Daimao's Henchmen
1. All killed by Goku except one, who was killed by a hungry Yajirobe
 
Raditz
1. Killed by Piccolo while Goku held him The beam ripped right through his, and his brothers chest.
 
Red Ribbon Soldiers
1. Countless numbers of them were killed by Goku in Dragonball
 
Spice Boys
1. Mustard - Killed by Gohan. Beat up Gohan's friend, Krillen, and was punished by getting killed with a Masenko.
2. Salt - Killed by Gohan. Angered Gohan so much that he lashed out, and blasted him with a Masenko.
3. Spice - Killed by Gohan. Got the kid mad by beating up Krillen, and paid the price by getting Masenkoed.
4. Vinegar - Killed by Gohan. Got the kid mad and was blasted with a Masenko.
 
Tao-Pie-Pie
1. Killed by Tien after coming back as a cyborg to try and avenge his previous defeat against Goku
 
Zarbon
1. Killed by Vegeta. He transformed, but was still unable to defeat the mighty Saiyan, getting blasted into a lake.