Apple has today announced updates to the entire iMac family. http://www.apple.com/au/imac/
Most notably, the company has brought Retina to the 21.5 inch iMac range, with 4K resolution displays. Apple has also dropped the non-Retina 27 inch iMacs, so they feature 5K displays across the board. The new iMac displays include faster processors, upgraded graphics, improved wider colour gamut and two Thunderbolt 2 ports. The new iMacs have launched alongside updates to the Magic Trackpad, Magic Mouse and keyboard.
Apple has announced the new Magic Trackpad 2, Magic Mouse 2, and Magic Keyboard. The new keyboard and trackpad have an updated design to accommodate improved keys on the keyboard and Force Touch on the trackpad, while the mouse has been redesigned internally. All three devices work on rechargeable lithium-ion batteries that juice up via a standard USB Lightning cable: http://www.apple.com/au/shop/mac/mac-accessories