You'd expect all characters to be human, but they're not. Do I have to explain this one? ;-)
Chars.- Yamcha, Chi-Chi, Krillen, Tien, Bulma, Chaoutzu
Most main char. are saiyans. Saiyans are born with the hunger for destruction and power. They love to fight and come from the planet Vegeta. Note- This includes char. with any saiyan heritage, even if they're half saiyan.
Chars.- Goku, Gohan, Goten, Vegeta, Radditz, Nappa, Broly, Paragus, Bardock, Pan, Trunks
Nameks are green men pink on their arms. Most of them are good-natured. On their planet, Namek, there are no females.
Chars.- Guru, Piccolo, Dende, Kami, Nail
There are some chars. in DBZ that species are unknown. It'd be pretty much impossible to name all of them, but I'll give you a few.
Some Chars.- Frieza, Mr. Popo, Zarbon, Dodoria, Garlic Jr., etc.
There's only a few androids. Five, if you don't count the ones in DBGT, DB, and Cell. Most of them appear after King Cold and Frieza are destroyed.
Chars.- #16, #17, #18, #19, #20, Cell (kinda).
Saibamen don't have names, and only appear once in DBZ, so it'd be pretty useless trying to make a char. list. They're green and are made from seeds, that, once planted, grow up to be Saibamen. They also have the tendency to be a Kamekaze, something we haven't seen much of since WWII ;-).
There's only one demon- Buu. That's if you don't count Fat Buu, Super Buu, Majin Buu, Kid Buu, well, you get the idea. Anyway, they're all pink. And not very nice at all (with the exception of Fat Buu making friends with Mr. Satan).
Chars.- The Buu Family