Topic: Proper list of seasons
Because there's some confusion about the proper listing of the series, let's have a simple list.
How you should watch Spartacus:
Season 1: Blood & Sand (aired from January 22 to April 16, 2010)
Miniseries/prequel (Season 1.5): Gods of the Arena (aired from January 21 to February 25, 2011)
Season 2: Vengeance (to be aired in January 2012)
Important!
DO NOT watch the prequel series before the first season, although chronologically it's the earliest with the story, it has plot stories, that reveal a lot for season 1.