Superscripts in bibliography with bibtex

The cite package provides such functionality and works with the standard bibliography styles such as unsrt.

\documentclass{article}

\usepackage[superscript,biblabel]{cite}

\begin{document}

Refering to second article\cite{art2} and then first article\cite{art1}

\bibliographystyle{unsrt}
\bibliography{test}
\end{document}

with test.bib containing

@Article{art1,
  author =   {Author, A. N.},
  title =    {Title One},
  journal =  {Journal},
  year =     2000
}

@Article{art2,
  author =   {Author, A. N.},
  title =    {Title Two},
  journal =  {Journal},
  year =     2008
}

yields

The first option superscript to the cite package affects the citations in the text, the second biblabel adjusts those in the bibliography.

You could use the natbib package and invoke it with the super option:

\usepackage[super]{natbib}

With this setup, \cite commands will generate citation markers as superscript-positioned numbers. Note that the natbib package is compatible with a wide range of bibliography style files, including the "original" BibTeX style files plain, unsrt, and alpha.

If you use the hyperref package as well, these superscript numbers will automatically be made into hyperlinks to the corresponding items in the bibliography.