For very simple file/content search i use total commander
For more advanced needs I have just recently got a project that needs me to search a lot in documents, so had that need again.
I tried archivarius but I struggled with the way it presents the results. I have to search several hundred times in a pot of documents to find date/price of purchase of something. Might be in a spreadsheet, might be in a pdf or a letter. I would have loved it if archivarius showed me just enough of the results that I didnt need to open the document. Also had a lot of stuff indexed I didnt want indexed, it's almost too good and sees too many things. Instead of spending the time to tweak the config, i went to look for something less powerful that would work out of the box for my needs
Right now I found docfetcher,
http://docfetcher.sourceforge.net/en/index.html , an open source beta tool. It does less document types and is more focused in searching through defined sets than all your documents, but it's quite useful. If it stays useful through this it will get my February project donation, else I'll go give archivarius another try.