MLA / APA Citation
 

 
These are online resources that "build" citations for you when you input information. You should always check the final citation against recent standards and what you've been shown in class.
Keep in mind that the purpose of citation is to give credit where credit is due, and to lead your audience to your original source.
 Citation
 
BIBme
This project from Carnegie-Mellon makes citation shamefully easy...meaning you would be ashamed if you don't get it right.
EasyBib
 It's easy...
Citation Builder
 North Carolina State University
Citation Machine
 The Landmark Project
Knightcite
 A citation generator from Calvin College
Ottobib
 This generates citations for books if you have the ISBN
Wikipedia citation generator
 If your teacher lets you use Wikipedia they have their own citation generator
 

 Here are some more links with writing and citation information: