This site is incredible. Heard about it on lifehacker a while back and it is a great time-saver.
Google's "Search by image" option has been around for a while, but it only works if you already have an image ready. With this site, you can draw what you're looking for, and search right away. The interface is not very complex and it's hard to create something detailed, but it's great for identifying logos or finding something of a particular color.