Remove Indentation for a Single Paragraph

\noindent suppresses paragraph indentation when used at the beginning of a paragraph.
Also, you can always group things within a {} so that any settings within their are not in effect after the group.

\noindent
This is my paragraph 2 but is not indented since it was started with noindent.  Blah blah blah.

This is my paragraph 3 and is indented.  Blah blah blah.

{\setlength{\parindent}{0cm}
This is my paragraph 4 but is not indented since parindent was set to 0 within this group.  Blah blah blah.
}