The iPhone 5 looks similar to previous models but with some improvements below.
Same width but taller 4-inch screen, 18 percent thinner and 20 percent lighter
Use Nano-SIM card and Lightning connector
Phone body made with aluminum and glass, support 4G LTE, up to twice as fast with A6 chip
Earbud-style headphones
Camera to shoot Panorama
iPhone 5 will come with the new iOS 6, see list of new iOS 6 features here:
http://shareah0lic.blogspot.sg/2012/06/what-is-new-in-ios-6.html
See the iPhone 5, iPhone 4s and iPhone 4 comparison here:
http://www.apple.com/iphone/compare-iphones/