Agent Ransack (the free version) is my goto tool for doing deep searches. It integrates with Explorer, has a decent interface, and is very fast (even spools up multiple threads if you have a multi core machine).
Plus, it can use regex's or normal search expressions, and can show context in the results pane.
It's not an indexed search app (so there's no "indexing" pain), so that means it's typically more useful if you have a folder structure where you can narrow down what to search by starting at a particular folder.
http://www.mythicsoft.com/page.aspx?type=agentransack&page=homethe paid version adds a few bells and whistles but ymmv
And finally, I use a filename only search called Locate32
http://locate32.netIt's also good for what it's intended, but the dev is more or less ceasing development on it.
It is open source though.