qlmanage is a CLI tool that, from the manpage, is a 'Quick Look Server debug and management tool.' It's got more options than described below, but those are for developers debugging QL.
The -p option generates a preview, as if you'd tapped the Space bar in the Finder. The -t option generates thumbnails, like in Coverflow or Info For. Here, then, are typical uses of the tool:
- qlmanage -p '/Users/Name/Music/Player.mp3'
Generates a QL window in Terminal. - qlmanage -t '/Users/Name/Pictures/Image.png'
Generates a window with a thumbnail. - qlmanage -p '/Users/Name/Documents/Nurse.doc' '/Users/Name/Movies/Liters.mpg'
Generates a QL window in Terminal with a page-through option to see both docs.
[crarko adds: I tested this, and it works as described. The Quick Look window that opens displays a [DEBUG] tag in the title bar along with the file name. As mentioned in the comments section, this previous hint shows this was also available in 10.5. ]

