Mail.app and the iPhone natively support Exchange if you're into that. iPhone support is great in my experience. I love Outlook 2010, which I'm beta testing.

Mail.app and the iPhone natively support Exchange if you're into that. iPhone support is great in my experience. I love Outlook 2010, which I'm beta testing. Mail.app was just too buggy for me and I like being able to have a shortcut key to file email and the rule support is just so much better in Outlook. I also prefer OWA to gmail, but don't use either.