ContactOffice allows you to check your e-mail with your favorite e-mail client with POP3 and/or IMAP4. So if you’re still using Microsoft Outlook for mail, you might want to take a look at Xobni (it’s a weird name, but it’s basically just ‘inbox’ spelled backwards).

Xobni is an Outlook plug-in that creates a sidebar in Outlook that automatically tracks contacts and organizes e-mails into fully searchable threaded conversations linked back to those people.

E-mails can be searched as independent threads or viewed in the context of a contact’s profile. The profile shows basic contact info (automatically updated) and a full history of threaded conversations, files, and people they’re connected to (the email “social graph”).

Xobni is invite-only for the moment, but will probably be opened up in the near future.