marginpar text alignment

This automates Ben Stern's answer using the KOMA Script test \ifthispageodd (through scrextend given the use of the book class) and defining an \alignedmarginpar which aligns right on left pages.

\documentclass[twoside]{book}
\usepackage[paperheight=5in,paperwidth=6in,top=.7in,bottom=.7in, inner=1in,
 outer=2in, marginparsep=.1in, headsep=16pt]{geometry}

\usepackage{scrextend}
\usepackage{lipsum}

\newcommand{\alignedmarginpar}[1]{%
    \ifthispageodd{%
        \marginpar{\raggedright\small #1}}{%
        \marginpar{\raggedleft\small #1}}%
    }

\begin{document}

\alignedmarginpar{This is the outside margin. I would like it to be aligned left (as it is).}\lipsum[1]

\clearpage

\alignedmarginpar{This is also the outside margin. I would like it to be aligned right.}\lipsum[2]

\end{document}

Put a \raggedleft right before your \marginpar text.

\documentclass[twoside]{book}
\usepackage[paperheight=5in,paperwidth=6in,top=.7in,bottom=.7in, inner=1in,
  outer=2in, marginparsep=.1in, headsep=16pt]{geometry}

\usepackage{lipsum}

\begin{document}

\marginpar{This is the outside margin. I would like it to be aligned left (as it
  is).}\lipsum[1]

\clearpage

\marginpar{\raggedleft This is also the outside margin. I would like it to be
  aligned right}\lipsum[2]

\end{document}