From Macrumors.com, here is a list of features:

-iPhone 4S. Outside the same, inside all different. A5 chip inside, dual-core graphics up to 7x faster than iPhone 4.
- Mike Capps from Epic Games on stage for demo. Showing off Infinity Blade 2.
- Phil back on stage. iPhone 4S battery has 8 hours of 3G talk time, 6 hours 3G browsing.
- Wireless system updated. Stainless steel band with two antennas, switch intelligently between them.
- Data speed twice as fast...14.4 Mbps HSDPA. It's what competitors call 4G.
- World phone...both CDMA and GSM in one phone.
- New camera system. iPhone 4 is top camera on Flickr. We wanted to make the 4S better than point and shoot.
- Eight megapixels...3264x2448. Backside illuminated sensor...73% more light per pixel than iPhone 4. 33% faster capture. Hybrid IR filter, better color accuracy and uniformity. Five element lens, 30% more sharpness, f/2.4 aperture. Face detection, better white balance, and fast photos.
- Time to first photo: 1.1 seconds. Half a second for next shot.
- Schiller demoing photos taken with iPhone 4S. 1080p HD video recording, video image stabilization, noise reduction. Wrapping up camera discussion.
- AirPlay mirroring. Gaming on the TV screen...wired or wireless.
- iPhone 4S pricing: $199 16 GB, $299 32 GB, $399, 64 GB, with contract. Black and white versions available.
- 8 GB iPhone 4 at $99, 8 GB iPhone 3GS free.

This doesn't really impress me much as I am an Android kinda guy, but maybe you Apple fanboys like it.