\documentclass[12pt]{article}
\usepackage{tabls}
\begin{document}

\begin{tabular}{|c|c|}\hline
	blah & $\sum_{i=1}^{100}i$\\\hline
	x & y\\\hline
	blah & $\sum\limits_{i=1}^{100}i$\\\hline
\end{tabular} 
\end{document}