All-new box with App Store and Siri support.
New iMacs Released [Update]
Photo from Appleinsider.com
-Up to 2.8 GHz Core 2 Extreme Processor
-Up to 4 GB Memory
-ATI Radeon HD Graphics
-Up to 1 TB Hard Disk
-Wireless 802.11n and Bluetooth 2.0
Also, Apple indicated that the keyboard that was previously leaked is indeed the new keyboard for the iMac.
Word of the iMac redesign first appeared in March from AppleInsider, though ThinkSecret was later able to corroborate the story and provide an exact date of release.
The new iMacs are available from the Apple Store (UK Store).
Update: Appleinsider has posted an extensive gallery of images of the new iMacs.