Yahoo lets users search e-mail photos, documents - Yahoo! News: "Moving beyond simple keyword searches, Yahoo will now allow users to trawl through e-mail files in far greater detail. Searches can focus on subject lines, the body of text and even attached documents, without first having to open the e-mail."
I saw this "New" link in my Yahoo email and tried it out yesterday. It looked useful. It showed all the attachments that were buried in my Inbox and folders, some that I had forgotten about. Check it out.