My favorite innovation on the Treo 700w was touchscreen photo speed dial. Instead of a list of names, you have a grid of faces you can tap to call. The iPhone, mysteriously, doesn't take advantage of its gigantic and gorgeous screen to do the same. That's a pity, too, because I can recognize the face of the person I want to call much more quickly than I can their name.
Step 1: Make a bunch of thumbnails of the faces of your favorite contacts. Upload them to a server (or Flickr, or wherever) and copy their image addresses.
Step 2: Go grab use the little hack here to add speed dial links to your home screen, but as the "Advanced" instructions suggest, paste the URL of your favorites' face thumbnails (from step one) onto the end. (No Jailbreak required)
Step 3: Move all your cute photo speed dial faces onto their very own Home Screen page. Voila, you can now hit the home button, swipe over to your speed dial screen, and there are up to 16 faces per page you can dial by tapping.
(Thanks to rener for the inspiration!)