http://nitrodesk.com/
Exchange support, albeit a little limited at the moment. But this one's the first public available. What's cool is, it's only 20 bucks right now (normally 30). I've been using it for a couple days now, and while it's not perfect (we're still on an Exchange 2003 server), it's definitely a step in the right direction.
Apparently, there's also this one, but I haven't tried it.
http://moonrug.com/android/index.html