You can do this in several ways: for example, by using an empty optional argument for \item (as Jake suggested), or by using the enumitem package to use an empty label, or by redefining \labelitemi; these approaches are illustrated in the following example:
\documentclass{article}
\usepackage{enumitem}
\begin{document}
\begin{itemize}
\item[] First.
\item[] Second.
\end{itemize}
\begin{itemize}[label={}]
\item First.
\item Second.
\end{itemize}
{\renewcommand\labelitemi{}
\begin{itemize}
\item First.
\item Second.
\end{itemize}
}
\end{document}
