Including line numbers in typeset output
For general numbering of lines, there are two packages for use with LaTeX, lineno (which permits labels attached to individual lines of typeset output) and numline. (Numline is considered obsolete, but remains available from the archive.)
Both of these packages play fast and loose with the LaTeX output routine, which can cause problems: the user should beware…
The vruler package sidesteps many of the problems associated with line-numbering, by offering (as its name suggests) a rule that numbers positions on the page. The effect is good, applied to even-looking text, but is poor in texts that involve breaks such as interpolated mathematics or figures. Documentation of the package, in the package itself, is pretty tough going, though there is an example (also inside the package file).