I love LaTeX, and I especially enjoy drawing diagrams in tikz.

Here is a stripped down version of my preamble with some of my most used packages:

\usepackage{amsmath,amssymb,amsthm,amsfonts,bm}
\usepackage{array} % for better arrays (eg matrices) in maths
\usepackage{color}
\usepackage{graphicx}
\usepackage{float} % To get the placement H for figures
\usepackage{tikz,pgfplots}
\usetikzlibrary{positioning,shapes,shadows,arrows,fit, decorations}
\usepackage[a4paper,top=1.75truecm,bottom=1.75truecm,left=1.75truecm,right=1.75truecm]{geometry}
\usepackage[parfill]{parskip}
\usepackage[bookmarks]{hyperref}
\hypersetup{colorlinks=true, pagebackref=page, citecolor=blue, menucolor=red}
\usepackage{natbib} 
\usepackage{hypernat} 

Another package I find really useful but that is not there is standalone.