It's the 4th of July weekend, which means sun for most of us and all kinds of fun outdoor activities, many of them including squirt guns. If you're hardcore, you use nothing but the Super Soaker, which was first introduced in 1989 and has evolved into personal water cannons that seem capable of blasting holes in concrete. Hyperbole aside, they've come a long way, and iSoaker has a very cool interactive, clickable chart showing the evolution of the world's most popular water gun. Which one was your favorite? [iSoaker]