This tool lets you search for a person's full name and phone number (and sometimes returns their address as well). Depending on the search, the tool may return "close matches" i.e. people with email addresses similar to the one you searched for.
You can use this tool to find a person's name, (partial) address and phone number from their email address. If you only search for a partial email address, InfoSpace will disguise the full email address of each person returned by a search, but you can communicate with them via a web form.
Beyond the above tools, you can also try typing the full email address of the person you're looking for into Google or Yahoo - you never know, you might get lucky and turn up a reference to them somewhere on the Web... Or perhaps they post on USENET? You can search on Google Groups to find out.