"Agent Ransack is a free tool for finding files and information on your hard drive fast and efficiently. When searching the contents of files Agent Ransack displays the text found so you can quickly browse the results without having to separately open each file!
Agent Ransack provides compelling advantages over similar search tools: Regular expressions that allow complex rule based searches. Immediate contents results view. Various wizards to walk the user through the searching process."
or, there is also File Invader, which seems to be nice, though perhaps not as fancy as Agent Ransack.