FUN FUN LOOP:
txt = "a";
while(1){
txt = txt += "a"; //add as much as the browser can handle
}
//[evil laugh] BOOM! All memory used up, and it is now CRASHED!
http://jsfiddle.net/DerekL/M45Cn/1/

Sorry for the Chinese characters…
Extra
Fun Fun Loop also works on Firefox!

And I have to give an applause to Safari, because it automatically reload the page when it is about to crash! Good job Webkit developers!
Oh yeah…
WARNING: Don’t try it in Internet Explorer… Because it crashed not my browser, instead, it crashed my Windows 7…

Yes. I have to restart the computer after that thing.