Gun-Shots.net has a list of sites offering printable targets for firearms practice in various formats, including PDF and Microsoft Word's .doc format. Some sites on Gun-Shots.net are defunct, but several were still online as of June 2015. Targets.ws has a big variety of targets in .gif and PDF formats.
For people who don't have software to open PDF or .doc files, VarmintHunters.com has targets in .jpg, .gif and .bmp formats.
Targets.ws offers several dozen printable targets in .gif and PDF formats. The site has sight-in, bulls-eye, animal and star targets and human silhouettes.
HWSportsman.net has 21 targets in PDF and .doc formats.
Targetz.com has 147 targets in PDF format.
Murraysguns.com offers compressed .zip files with targets in PDF and .doc formats.