How to number several equations with one number

\begin{eqnarray} 
 \begin{array}{rl}
    &x = foo \\
    & y = bar
 \end{array}
\end{eqnarray}

 I sometimes get that I should not use eqnarray that extensive, but it works for me.
Another solutions with equation and aligned environments here.

Avoid eqnarray

Some say, you should avoid eqnarray in multiline equations. There are several reasons why and how to do that, see here:
http://tug.org/pracjourn/2006-4/madsen/madsen.pdf

I personally used eqnarray a lot, and never had problems with that till now, when it just generated too much empty space before and after the equations, so I simply switched to array.