TechRadar has a great post on early Windows 7 concepts that didn't make the cut— where they originated and what actual features they directly influenced—such as the "Bat Signal", which became Aero Peek.
There were apparently over 400 concept sketches shown off at the MIX conference, an event for developers where Microsoft spoke on the development process for Windows 7.
Bat Signal was a taskbar thumbnail preview that projected the window you mouse-hovered over up onto the desktop like a spotlight. Aero Peek, as you may know, now just pops up directly above the taskbar, with a much smaller thumbnail.Another feature, Aladdin, was the inspiration for Aero Shake, and essentially let you preview a background window by rubbing it with the mouse cursor.
There were other tweaks made as well, like scrapping thumbnails in the taskbar how they finally decided to make Jump Lists a right click function (they conducted user testing). It's a pretty neat article, all in all, and you should check it out at [TechRadar via Neowin]