You can also use, inside your org file, the below option:

#+OPTIONS: html-postamble:nil

To view most of existing html export options, type C-c C-e # html RET in org buffer and it will insert the template of HTML options.

2014-01-21 : There is another way to answer the initial question, not yet described in any other answer. File local variable org-html-postamble set to nil. This can be done with M-x add-file-local-variable RET org-html-postamble RET nil RET. This will add lines like the following to the end of file.

# Local Variables:
# org-html-postamble: nil
# End: