Add GCal and GDocs Gadgets
In Gmail Labs, you'll find the option to add "gadgets" for your Google Calendar and Google Docs to the sides of your Gmail inbox. These aren't exactly brand-new features, but they are essential. These widgets give you a snapshot of your schedule and cloud-stored files that comes in handy when making new appointments or collaborating via email. There's even one-click capability to add a calendar event from your inbox.