Remove section number from Table of Contents

Question

How can I remove section numbers from the Table of Contents? My document class is article:

\documentclass[a4paper]{article}
\begin {document}
\tableofcontents
\section{one}
test text number one
\section{two}
test text number two
\end{document}

Answer 1

Following Astrinus's advice, you can add the two lines of code between \makeatletter and \makeatother, given in egreg's answer, to modify the entry in the table of contents. Here is how you can do this:

\documentclass[12pt, a4paper]{article}

\makeatletter
\let\latexl@section\l@section
\def\l@section#1#2{\begingroup\let\numberline\@gobble\latexl@section{#1}{#2}\endgroup}
\makeatother

\begin{document}
\tableofcontents
\newpage
\section{One}
test text number one
\section{Two}
test text number two
\end{document}

Notice that you should insure a \newpage is there after the \tableofcontents

Answer 2

You can easily do that with the titlesec/titlestoc package. It has commands that allow for a different formatting of numbered and unnumbered sections (if you want to add unnumbered sections) in the table of contents:

\documentclass[a4paper]{article}
\usepackage{titletoc}
\begin {document}
\titlecontents{section}[0em]
{\vskip 0.5ex}%
{\scshape}% numbered sections formatting
{\itshape}% unnumbered sections formatting
{}%
\tableofcontents
\section{A First Section}
Test text number one.
\section{Another Section}
Test text number two.
\section*{An Unnumbered Section}
Test text number three. 
\addcontentsline{toc}{section}{An Unnumbered Section}
\end{document}