One of my favorite things in eM Client is the Agenda view in the sidebar.
It is way ahead of the today pane in my favorite email application - you know the one. That I can view events further than 4 weeks ahead does it for me, but other options like choosing which folders to appear in Agenda really sells it. And it just looks great. Simply wonderful!
Now if those few little bugs can be sorted, eM Client could be tipped to be my favorite email application.