Business letter - basically letter.cls, but with everything left-aligned

letter.tex

\documentclass[12pt]{letter}

\usepackage{fullpage} %1in margins on every page

\longindentation=0pt
\renewcommand*{\opening}[1]{\thispagestyle{empty}%
  {\raggedright \fromaddress \\*[2\parskip]%
    \today \\*[2\parskip]%
    \toname \\ \toaddress \par}%
  \vspace{2\parskip}%
    #1\par\nobreak}

\signature{Your Name}
\address{123 Some St \\ Anytown, MA 01000}
\begin{document}
  \pagestyle{empty}
  \begin{letter}{Recipient \\ 456 That Avenue \\ West Anywhere, IN 47000}
    \opening{Dear Mr Recipient:}
    
    \closing{Sincerely,}
  \end{letter}
\end{document}
% vi:wrap:textwidth=80:wrapmargin=2

One downside is that the unmodified "letter" documentclass allows the \author{} tag to be optional. This one doesn't. I might try to fix that some day.