One of the oldest physical things proving man's intelligence is tools, and when we find them on archaeological digs we then attribute a certain amount of cleverness to whatever tribe's bones we found them under.
I am fascinated by modern tool design. Now that adjustable wrenches, sheetrock screws and power drills have been long established, modern tool design largely revolves around making existing tools faster, more efficient, and/or safer, like the Eurekazone cutting system or the Kreg Pocket Hole Jig.
Another area of tool design focuses on clever little items that enable you to do more with less. As an example, when driving screws in something you often have to pre-drill a hole, then grab a second tool to drive the fastener in. So you have to carry two gun-shaped things that both do essentially the same thing, rotate a bit at high speeds. Solving this is Eagle Tool Company's Sheet Metal Installation Tool (spotted on toolmonger), a combination drill bit and driver attachment that transforms from one to the other by means of a sliding collar, which means you now only have to carry one tool.
A second device along these lines is Jorgensen's ISD clamps, which look like other pistol-grip clamps but have a neat little trick: You can connect two of them together to make an even longer clamp, so you don't have to go to the store to buy an extra clamp for those odd jobs spanning greater distances.