How can I easily view contents of attachments displayed as icons?

To quickly preview attachments in a message including those displayed as icons, press ⌘+Y. A QuickLook preview will appear and you will be able to move among the attachments using arrow keys and dismiss the preview using space bar. Alternatively you can first select a particular attachment and then press ⌘+Y. This works both when reading and composing messages. The feature is independent from Attachment Tamer and is also available via File menu.