dnGREP - dnGrep allows you to search across files with easy-to-read results.
SearchMyFiles - Alternative to the standard Search For Files And Folders module of Windows. Duplicates search is also supported.
AstroGrep - AstroGrep is A Microsoft Windows GUI File Searching (grep) utility.
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, ...
Agent Ransack - Agent Ransack is a tool for finding files and information on your hard drive fast and efficiently.
FAR - Find And Replace - FAR is a simple tool for search and replace operations over multiple files.