Not sure when this feature was added, but I’m running the Inkscape 0.47 preview and discovered that the default install now includes a “Printing Marks” feature. You can access it from the main menu:
Extensions > Render > Printing Marks
Extensions > Render > Layout > Printing Marks
The small options window that pops up allows you to adjust a variety of settings for the position of the marks as well as the type of marks to be displayed, seeming to cover all of the needs of a typical commercial printing process.
The “Live Preview” option makes it easy and efficient to adjust the settings to match your desired output. Once you hit Apply the specified marks are added to your document as vector art in a new, locked layer titled “Printing Marks”.
In the past I’ve manually created crop marks when needed, but this is a major step on the road to serious recognition and use by graphic design professionals. Eventually it would be great to see these options removed to a print and/or export dialog interface, but this is an excellent option to have as well.
Inkscape is an open source and free application built around the SVG recommendation that makes it easy to create vector images. I use it to create illustrations as well as single-page layouts of all sizes. In fact, I recently created a business card layout with Inkscape, exported as PDF and sent to a printer to create offset business cards. The cards turned out great without any problems. A serious vector art tool.