UPDATE: I have purchased Airmail from the mac app store. So far Airmail supports IMAP, Exchange, POP3, email accounts (Google, mac.com, me.com, icloud.com, yahoo.com, as well as my website email). The App is $1.99 in the apple app store. So far it has preformed very well over all. I love the interface or UI!. I believe Airmail is just as good or better than the built in Mail.app! It is very easy to use.
UPDATE: Exchange support is here, POP3 is here (current release 1.38) update via the App Store!
NOWYOU CAN GET AIRMAIL 2.0 for $9.99 at the app store ( I don't think the app isworth more than $2.99 )