All-new box with App Store and Siri support.
iPhone 3G S Has a 600 MHz Processor, 256MB of RAM, PowerVR SGX
600 MHz is notably faster than the current iPhone and iPod Touch which run at 412 MHz and 532 MHz, respectively. Until now, the 2nd Generation iPod Touch has been the fastest device in the lineup by a good margin. Meanwhile, the previous generation models where also limited to 128 MB of RAM, so the new device offers twice as much which could be a welcome change to developers. The processor/ram information seems to confirm many details that were first revealed in a Chinese forum post.
Apple has been particularly unrevealing about the detailed hardware specs for the new iPhone even to developers at WWDC. The new iPhone is also believed to use the new PowerVR SGX graphics processing unit which provides support for OpenGL ES 2.0. This notably improved performance may require developers to support these multiple device capabilities within their apps.
For those interested in more of a technical analysis, Anandtech offers a detailed breakdown of the new iPhone's processor and GPU, according to their sources. The information lines up with the other reports referenced above.
Although unannounced, the iPhone 3GS uses (again) a Samsung SoC but this time instead of the ARM11 + MBX-Lite combo it's got a Cortex A8 and PowerVR SGX; just like the Pre.