There are several tools for indexing files on a computer to allow full text searches.
The classic of course is grep, but it doesn't generate any index, so it gets slow when searching through lots of files. In addition, it doesn't work well with non-ASCII files like OpenOffice documents, pdf or ps files and the like.
There is a list (not Debian specific) at http://www.antezeta.com/desktop-search.html .
Discussions and comparisons:
http://www.freesoftwaremagazine.com/blogs/desktop_search_tools_gnu_linux_tracker_recoll_strigi_deskbar Desktop search tools for GNU/Linux: the competition hots up - Tracker, Recoll Strigi and Deskbar
http://linuxappfinder.com/utilities/search Search tools @ Linux App Finder
http://www.linux.com/articles/114283 Recoll: A search engine for the Linux desktop
http://www.osnews.com/comment.php?news_id=17763 Recoll: a Search Engine for the Linux Desktop
No Debian package yet: