My experience (some years back) of reviewing hundreds of resumes and
job applications tells me: One page resumes are fine - so long as
they are attractive and easy to read.
If your resume, in reasonably size print, covers two pages, be proud
that your accomplishments cannot be confined to one page. Trying to
squeeze two pages into one -- with tiny print, no spaces between
paragraphs, no margins, etc - makes them ugly and hard to read. You
are being hired to make things EASIER on the boss, an impression you
won't make if your resume is HARDER to read than the others.
However, I do not recommend resumes 3 pages long. (I imagine that
there are situations and positions for which lengthy and detailed
resumes are required and resumes longer than two pages are welcome,
but such situations are not common.) If your resume threatens to
spill over onto a third page, I suggest reducing the jobs that were
long ago, or unrelated to the skills required for the job you're
seeking, to one-liners. Even so, keep the margins and typefaces from
shrinking.