Human: A Human is one of the weaker races in DB/DBZ/DBGT. They are just like you and me but some there are some Human (like Krillian) that have the abilities to use Ki and fly.
Tsfurujin: This is a different race that lived on Planet Vegeta (was called Planet Plant). They where wiped out by the Saiyan's as they took over that planet. Later in DBGT there was one left, his name was Babi. They look weird.
Saiyan: This is the most famous race in DBZ/DBGT. They are born with tails and a strong love to kill. Goku seemed to be a little brat but then hit is head so he had forgotten all of his anger and rage. When a Saiyan, with a tail, sees the light of a full moon he will transform into an ape like form. Saiyan's can also transform into a Super Saiyan (there are different levels of the Super Saiyan of SSJ for short)
Namekian: Nameks are peaceful creatures. There have only been about 2-3 evil Nameks (Piccolo Daimoah, Piccolo Jr. and Slug). They are green with 2 little antenna coming out of their head. Their body looks cool because their muscles is on the out side. The Nameks have two really awesome and useful techniques which are the abilities to rehabilitate limbs and other body parts and the ability to make their body grow and limbs stretch!
Majin: Majin's are any race but they are evil and are being controlled by Bibidi. Vegeta once was a Majin as well as Buu was. All Majins have the "M" marking on their body (usually on their forehead).
Android: Androids are artificial humans. Their power is much greater though. Some of the androids where stronger than SSJ's at one point (but are surpassed by the mighty Saiyan's).
Changeling: Changelings are strange creatures that transform to become stronger. They are evil and strong.
Arlia-jin: They are look sort of like cricket . They come from Planet Arlia. They where wiped out by Vegeta.
Kaioshin: Kaioshins are the gods of gods. They don't all look the same but some of them do. They are strong, not as strong as SSJ's (their not ever close to the power of the Saiyans, or as strong as the mightiest Namek, Piccolo! ).
Kaio: Kaios are gods. They all where pretty much the same thing and have a symbol on their shirts.
Saibamen: Saibamen are really cool. They spit acid from their heads and they are evil. They are kinda weak. (average power level of 1000) Guardian: The Guardian's (of earth) are strong but only in the field of magic. They all wear druid like clothes (with hoods and such) and all you can see are the Guardian's glowing red eyes through their hoods. The only Guardian's who weren't like this were Kami and Dende.