You can drag disk images in the left window pane, just below the line under the disks. When you drop it, Disk Utility makes an alias to that image. It remembers these aliases even after you quit. After you've added the image, you can easily burn, verify and repair it. The disk image path at the bottom becomes clickable for mounting it as well.
One other useful functionality is that you can place a disk restore image in the pane, after which you can easily drag it to the Source field in the Restore tab.
Update: As noted in the comments, to remove the image, simply drag it off the list.

