I've found an example here but that only centers one column and I can't really adapt it to my needs. What I'd like is something like this:

I've found an example here but that only centers one column and I can't really adapt it to my needs. What I'd like is something like this:

On
You'll need \usepackage{array} to do this.
From what I can gather, you're looking at the m{} alignment, which wraps a paragraph at the specified point value, and vertically aligns the text to the middle of the field. For example, something like this:
\begin{tabular}{|m{2cm}|m{1ex}|m{1ex}|m{1ex}} \hline
& x1 & x2 & x3 \\\hline
Long Label & 1 & 0 & 1 \\\hline
Long Label & 0 & 1 & 1 \\\hline
\end{tabular}
Try this:
For more info on table formatting see http://en.wikibooks.org/wiki/LaTeX/Tables
EDIT: changed c to b{}