Description list with aligned descriptions

This is one possibility:

\documentclass{article}  
\usepackage{calc}  
\usepackage{enumitem}  

\begin{document}

\begin{description}[leftmargin=!,labelwidth=\widthof{\bfseries The longest label}]
  \item[The longest label] text
  \item[Short]  long long long long long long long long long long long long long long long long long long long long long long long long long long long long long long text
\end{description}

\end{document}