Not being snarky here, but how about gmail? If you want pop3 or IMAP, you can do that in gmail. You can also tag/color e-mails based on which address they're coming from, set up reply-to, have a huge amount of space for archiving, Google searching for your e-mails...

Postbox is a nice alternative, though it is made from Thunderbird code by many of the people from the Thunderbird team. Still, they made the user experience much better...

Check it out at http://www.postbox-inc.com/, and there's a free, Express version available too.

You should mention your platform, but in general, no. Email clients are in a perfect storm of unsexy, mostly solved, and difficult to make money from.