From Gizmodo, a camouflaged iPhone 4 pulled apart to reveal lots of interesting things:
• Front-facing video chat camera
• Improved regular back-camera (the lens is quite noticeably larger than the iPhone 3GS)
• Camera flash
• Micro-SIM instead of standard SIM
• Improved display.
• What looks to be a secondary mic for noise cancellation, at the top, next to the headphone jack
• Split buttons for volume
• Power, mute, and volume buttons are all metallic