I was looking for the same thing as you and haven't found anything yet. Obviously, the Windows 8 Store is still in it's infancy, so it's worth checking again from time to time. Currently, I'm using a combination of Outlook 2013 (ok, it's not a Windows 8 app...), gSyncit, and toodledo Pro. I don't particularly recommend it, but it does the job for now. But I will certainly reassess this as other possibilities emerge.