Varies according to severity and intrinsic host factors (immunosuppression, etc.).
Diarrhea that develops during antibiotic use or within 2 weeks of discontinuation
Usually occurs after 7-10 days of antibiotics, as diarrhea before that time is more often poor tolerance to antibiotic
Recent discharge from hospital
Profuse watery diarrhea
Abdominal pain/tenderness
Fever
At the extreme, may present with sepsis secondary to intestinal perforation or toxic megacolon
Clostridium difficile 
Viral 
Salmonella
Bacterial
Campylobacter jejuni
Campylobacter
Yersinia enterocolitica
Shigella