Hi,
I needed a replacement for outlook 2003 and after searching about decided on Yahoo! Zimbra.
http://www.zimbra.com/products/desktop.html
It comes with 'Contacts', 'Calendar', 'Tasks' and other bits and pieces including multiple email account handling. And, it's free!
The things it doesn't have, unless I'm mistaken, is 'Contact Categories and Groups' but being open source this could be incorporated in the future, I'm sure.
Regards