These screenshots come courtesy of Microsoft. I'll be posting my own shots as well, but Microsoft's shots are interesting because they depict a slightly different build than the one distributed to PDC attendees. Thus, it features additional functionality such as the new Aero desktop effects and the new taskbar with jump lists and taskbar previews.
The Windows 7 M3 desktop with Aero Desktop Effects. Note that the version distributed at PDC lacks these effects, including the new taskbar.
Desktop Gadgets and Calculator.
New Show Desktop effect.
Windows Taskbar Previews: A new "peek" view of grouped open windows.
The Windows Media Player taskbar preview is interactive, with playback controls.
The Windows 7 M3 Start menu.
The Windows 7 M3 Start menu support pop-outs for icons so you can get to more places without mousing around.
Power management jump list.
Wireless networking jump list.
Desktop themes combine backgrounds, glass colors, sounds, and screensavers. You can make your own of course.