fadeToggle(). as suggested by Karl Swedberg in his jQcon talk. patched live! omg

src/effects.js

@@ -252,7 +252,8 @@ jQuery.each({
 	slideUp: genFx("hide", 1),
 	slideToggle: genFx("toggle", 1),
 	fadeIn: { opacity: "show" },
-	fadeOut: { opacity: "hide" }
+	fadeOut: { opacity: "hide" },
+	fadeToggle: { opacity: "toggle" }
 }, function( name, props ) {
 	jQuery.fn[ name ] = function( speed, easing, callback ) {
 		return this.animate( props, speed, easing, callback );

test/index.html

@@ -259,6 +259,9 @@ Z</textarea>
 
 			<div id="slidetogglein" class='chain test'>slideToggleIn<div>slideToggleIn</div></div>
 			<div id="slidetoggleout" class='chain test out'>slideToggleOut<div>slideToggleOut</div></div>
+			
+			<div id="fadetogglein" class='chain test'>fadeToggleIn<div>fadeToggleIn</div></div>
+      <div id="fadetoggleout" class='chain test out'>fadeToggleOut<div>fadeToggleOut</div></div>
 
 			<div id="fadeto" class='chain test'>fadeTo<div>fadeTo</div></div>
 		</div>

test/unit/effects.js

@@ -729,6 +729,13 @@ test("Chain slideToggle out", function() {
 	jQuery('#slidetoggleout div').saveState(jQuery.support.shrinkWrapBlocks).slideToggle('fast').slideToggle('fast',jQuery.checkState);
 });
 
+test("Chain fadeToggle in", function() {
+	jQuery('#fadetogglein div').saveState().fadeToggle('fast').fadeToggle('fast',jQuery.checkState);
+});
+test("Chain fadeToggle out", function() {
+	jQuery('#fadetoggleout div').saveState().fadeToggle('fast').fadeToggle('fast',jQuery.checkState);
+});
+
 test("Chain fadeTo 0.5 1.0 with easing and callback)", function() {
 	jQuery('#fadeto div').saveState().fadeTo('fast',0.5).fadeTo('fast',1.0,'linear',jQuery.checkState);
 });