I use the package enumitem. You may then set such margins when you declare your lists (enumerate, description, itemize):
\begin{itemize}[leftmargin=0cm]
\item Foo
\item Bar
\end{itemize}
Naturally, the package provides lots of other nice customizations for lists (use 'label=' to change the bullet, use 'itemsep=' to change the spacing between items, etc...)