We've covered using RefWorks to created citation lists (posted on March 20, 2006), using EBSCO to generate a citation (posted on March 27, 2006), so here are a few websites that offer citation builders.
The Citation Machine -- choose APA or MLA, choose from print or nonprint, enter your information and submit.
The Citation Builder -- This is an interesting utility. It generates both a citation for MLA & APA from the same information so that you can compare them.
KnightCite -- by far, my favorite. Select your style (MLA, APA or Turabian), the source type (print/electronic) & the resource (book, article, etc.) and submit.