Just after Christmas, I got onto an Outlook plug-in called Xobni ("inbox" spelt backwards) (via Lifehacker).
Xobni adds a new sidebar in the main Outlook window which provides a wide variety of relevant information on the sender of the currently-selected e-mail. This information includes the number of e-mails you've received from that contact, contact details, who else they've CC'd or been CC'd on in all e-mails indexed by Xobni, quick links to their most recent e-mails, and a list of files sent to or from that contact.
I've used Xobni for only about a week and a half as I've been on...