This is a list of frequently use packages:
(Usage: Insert \usepackage{package} before \begin{document})

fullpage: Use 1 inch margins

anysize: Set margins

\marginsize{l}{r}{t}{b}

multicol: Use n columns

\begin{multicols}{n}

graphicx: For displaying images

\includegraphics[width=3cm]{filename}

\includegraphics[width=0.50\textwidth]{filename}

url: To insert URL

\url{http://selinap.com}

hyperref: To handle cross-referencing commands in LaTeX to produce hypertext links in the document

The LaTeX Companion (Tools and Techniques for Computer Typesetting)