Gmail is set to get a redesign that brings it in line with the the visual UI of Google+. While the final redesign hasn't been pushed out yet, you can still apply it to your current Gmail setup using a theme that Google has made available. Simply log in to Gmail and go into your theme settings and choose either "Preview" or "Preview (Dense)" to apply the new hotness. What do you think of the new layout?
Oh, and it looks like Google Calendar picks up the redesign as well.