Newline in a table cell which is centered

How about using \shortstack inside a cell?

\documentclass{article}

\begin{document} 
\begin{tabular}{ccc}
    one & two & three \\
    one & two & \shortstack{a \\ bb \\ c}\\
\end{tabular}
\end{document}

This is an old thread, but there is a new solution.

\usepackage{makecell}
%% tablestart
...
\makecell{line 1 \\ line2}
%% tableend

If you want the cells to be centered horizontally as well as vertically I suggest the following solution:

\documentclass{article}
\usepackage{booktabs}
\newcommand{\bigcell}[2]{\begin{tabular}{@{}#1@{}}#2\end{tabular}}

\begin{document} 

\begin{tabular}{ccc}
\toprule
a & \bigcell{c}{this schould be a longer line \\ this is a shorter one} & c \\ 
\midrule
 0,9892 & 0,9892 & 0,9892  \\
\end{tabular}

\end{document}