I know this thread has been dormant for almost one year, but I would like to add my $0.02 anyway: KFind is a part of the KDE suite. As far as I know, it is installed by default on any kde installation. KFind can search for words, phrases, and strings within the following file types: Text, KWord, KPresenter, KSpread, OpenOffice.org Writer, OpenOffice.org Impress, and OpenOffice.org Calc. I use it to find references to topics within any of the several thousand .rtf files I have written. Admittedly, it would be nice to be able to search across PDFs, address books, and e-mail archives, but address books and e-mail archivers (at least) usually come with their own search engines, which leaves lacking only the ability to search for text across PDFs.