Q:

Whitespace before \cite that ends a sentence or a paragraph

If I summarize content from another source, I'll use \cite to reference the author. In natural sciences it seems to be standard to use \cite at the end of the sentence or paragraph that containts cited content.
Example:  
Lore ipsum \cite{OtherSource}.

Is there any recommended way about whitespacing before the \cite command? I could go with
Lore ipsum \cite{OtherSource}.

or
Lore ipsum\cite{OtherSource}.

Edit: My question is about, whether I should include a whitespace or not.

A:

For citation styles that typeset the content of \cite in the main text body (e.g., numeric, alphabetic and author-year styles) you definitely want a space before the citation, i.e.,
Lorem ipsum \cite{<key>}.

or (especially in case of numeric styles)
Lorem ipsum~\cite{<key>}.

For styles that move the citation content into a footnote (e.g., author-title and verbose styles), I recommend to use
Lorem ipsum.\cite{<key>}

Some European styles prefer the footnote mark before the punctuation, though (thanks to jon for the hint).
In case you use biblatex and its \autocite command, you may use
Lorem ipsum \autocite{<key>}.

independent from the actual style -- \autocite will move the footnote mark after the end-of-sentence period in case your style uses footnotes.

