List of Darkstalkers games:
Darkstalkers: The Night Warriors (America) or Vampire (Japan)
Night Warriors: Darkstalker's Revenge (America) or Vampire Hunter (Japan)
Darkstalkers 3: Vampire Savior (America) or Vampire Savior: Lord of Vampires (Japan)
Vampire Chronicle for Matching Service (Japan)
The first game consisted of twelve characters, though two were unplayable bosses:
Anakaris-The Pharaoh Mummy dude
Bishamon-The dark samurai
Demitri Maximov-The vampire
Jon Talbain (Gallon in Japan)-The werewolf
Lord Raptor (Zabel Zarock in Japan)-The zombie or ghoul
Morrigan Aensland-The succubus
Rikuo (Aulbath in Japan)-The merman
Victor von Gerdenheim-The Frankenstein's Creature
Huitzil (Phobos in Japan)-The robot, a boss character
Pyron-The Fire God or Alien or whatever, final boss
The second game was really more of a Super Street Fighter II to Street Fighter II comparison, because all it added were a few new moves, new characters, and made bosses playable. The endings were still the same.
The new characters included:
Donovan Baine (followed around by Anita)-The dhampir
Hsien-Ko (also known as Lei-Lei)-The ghost girl
The third game brought a new plot, new battle systems, and new characters:
Baby Bonny Hood/B.B.Hood (Bulleta in Japan)-Little Red Riding Hood with a tommy gun
Jedah-The Dark Master
Lillith-The younger succubus
Q-Bee-The giant bee lady
Oboro-Secret character, formerly was Bishaman until he freed himself from the armor
Shadow-Secret character, a phantom that possesses it's previous victim
Marrionette-Secret character, a puppet that has the moves of whoever she is fighting
Chronicle was only released in heavily limited supply in Japan for the Dreamcast. It was sort of a compilation game, but sort of not. It allowed you to pick a version of your character from any of the previous games, even if that character hadn't been in that game, and fight with the style and moves they had in that game. It also had online capabilities (hence matching service).
Some of the characters also appeared in Marvel vs. Capcom and Marvel vs. Capcom 2.
There was also a short anime OAV which consisted of four episodes. This is available on DVDs entitled Night Warriors: Darkstalkers Revenge ALPHA and Night Warriors: Darkstalkers Revenge OMEGA.
As for other merchandise, Darkstalkers can appear on mouse pads, lighters, figurines, mangas, and several other items, mostly in Japan.