The Google logo is probably the best and most important logo of them all. It shows great concept and really appeals to everything. Now the current logo was designed by an artist called ruth Kedar, and its a word mark based on the Catull typeface.
Google also does little modifications and just funny additions on special dates, like holidays, birthdays of famous people, and even major events like the olympics. The special logos are known as Google doodles.
In one of the older versions Google had an exclamation mark at the end of it to mimic the Yahoo! logo. The graphic designer who developed the now famous Google logo, said "We ended up with the primary colors, but instead of having the pattern go in order, we put a secondary color on the L, which brought back the idea that google doesn't follow the rules."

