From the press release:

Apple now offers a $999 Mac mini that is specially configured with Mac OS® X Snow Leopard® Server. Mac mini with Snow Leopard Server features two 500GB hard drives for a total of 1TB of server storage in the tiny 6.5-inch square by 2-inch tall Mac mini enclosure.

The standard Mac mini starts at $599 and features the same design as previous models. It now starts with a 2.26GHz Core 2 Duo processor, 2GB of 1066MHz DDR3 SDRAM, NVIDIA GeForce 9400M graphics, and a 160GB hard drive.

The server model is where the real news is. The new Mac mini server does not have an optical drive but instead has two 500GB hard drives. It comes with Snow Leopard Server pre-installed — this is clearly Apple’s answer to Windows Home Server. The Mac mini with Snow Leopard Server costs $999 and comes with a 2.53GHz Core 2 Duo processor, 4GB of 1066MHz DDR3 SDRAM, and NVIDIA GeForce 9400M graphics.

Previously:
10/20/09: Mac mini with OS X Server and Multi-Touch Trackpad for Desktop Macs
10/5/09: Mouse, iMac, and Other Apple Hardware
9/30/09: Updated iMac and Mac mini Coming in October