All the gangs I got information on are in here. I don't know a lot about the gangs but I got some decent information on them.

Cartel: The Cartel are another Hispanic group, they are in Stauton Island and Shoreside Vale. The woman who double-crossed you in the beginning of the game and her partner are the leaders of them. They look like cowboys and they carry M-16's.
Mafia: Their grounds is around Saint Marks in Portland. They are the first people you work for. 8-ball hooks you up with Luigi and you get introduced to the rest of the Mafia family. They carry shotguns and handguns. They are always dressed in nice suit.
Hoods
Nines
Jacks
Triads: This is a Chinese gang and their turf is in Chinatown located in Portland. They have a fish factory as a front and they also do protection jobs. They are enemies with the Mafia and they are in a turf war with them. The triads are dressed in blue and carry handguns and bats.
Yardies: This is a Jamacian gang who don't like the Diablos. King Courtney's missions consist of killing Diablos making the Diablos not like you. They carry handguns and bats. They are dressed in brown clothes.
Yakuza: This is a Japanese gang who don't like the Cartel. Their turf is in the Central Business district in Stauton Island. You work for them after you beat the mafia missions. Their front is a casino, they are dressing if the same clothes as the Mafia but not in black. They carry handguns also.
Diablos: The Diablos are a hispanic group who are kinda neutral. The Diablos hang out around Hepburn Heights in Portland. They have nice black jackets with their mark on the back. Their only weapons are thier fists or a bat but if you jump on a car they WILL shoot you with a gun(?).