jQuery “blinking highlight” effect on div?

Answer 1

jQuery UI Highlight Effect is what you're looking for.

$("div").click(function () {
      $(this).effect("highlight", {}, 3000);
});

The documentation and demo can be found here

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Edit:
Maybe the jQuery UI Pulsate Effect is more appropriate, see here

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Edit #2:
To adjust the opacity you could do this:

$("div").click(function() {
  // do fading 3 times
  for(i=0;i<3;i++) {
    $(this).fadeTo('slow', 0.5).fadeTo('slow', 1.0);
  }
});

...so it won't go any lower than 50% opacity.