How can I typeset non-inline math in tables?

You can add \displaystyle within the inline math environment, e.g.

\documentclass{article}
\usepackage{amsmath}
%\usepackage{fixltx2e}  % fixes that \( \) are fragile, but not necessary with recent versions of LaTeX
\begin{document}
\begin{tabular}{cc}
\( \lim_{x\to 0} \frac{\sin x}{x}   \) & \( \sum_{i=1}^n x_i \) \\
\(\displaystyle \lim_{x\to 0} \frac{\sin x}{x}   \) & \( \displaystyle \sum_{i=1}^n x_i \)
\end{tabular}
\end{document}

use tabularx or alternetively the p-column specifier if you want smaller columns:

\documentclass{article}
\usepackage{amsmath,tabularx}
\begin{document}

\noindent
\begin{tabularx}{\linewidth}{@{}XX@{}}
\[ test  \] & \[ test \]
\end{tabularx}

\end{document}