dtsearch - dtSearch - The Smart Choice for Text Retrieval since 1991.
SearchMyFiles - Alternative to the standard Search For Files And Folders module of Windows. Duplicates search is also supported.
DocFetcher - DocFetcher is a portable German/English open source desktop search application.
PowerGREP - Quickly search through large numbers of files on your PC or network using powerful text patterns to find exactly the information you want. Search and replace with plain text or regular expressions to maintain web sites, source code, reports, ...
dnGREP - dnGrep allows you to search across files with easy-to-read results.
Recoll - Recoll is a desktop full-text search tool. Recoll finds keywords inside documents as well as file names.