Gmail Labs has added yet another feature to Gmail, one that will come as a boon to anyone with a large screen monitor and wondering what to do with all that additional real estate. It's called Multiple Inboxes, and as the name implies, you can now sort your categorized email into multiple panes.
The Multiple Inboxes features makes it possible to configure up to five additional panes (labeled 0-4) positioned above, below, or to the right of your main inbox. With it, you could, for example, set up separate panes for unread emails, drafts, emails with attachments, labeled emails, and/or however you see fit using any of Gmail's supported search operators.
You'll find the Multiple Inboxes feature in the Labs tab under Settings. Once enabled, go into Settings, click Multiple Inboxes, and configure the panes however you like.