Flash
Previously a great way to manage the presentation layer of your yard. Tries to stay relevant by updating its wheels every now-and-then (at which point it tries to convince you to get a mule-powered tiller too. No thanks, just the wheels).
JavaScript
Can be used just about anywhere and you almost always need one.
jQuery
Faster than a regular screwdriver, but leads to laziness.
ASP.NET Web Forms
Had a purpose once. Doesn't any more.
ASP.NET MVC
You just needed a knife, but you got this.
Perl
Most people don't know what it is or what it is good for.
PHP
Good at moving stuff around, but overall it just blows.
CSS
Most of these are needed just to make your page work right in IE.
Node.js
Everytime you see it you want to play with it.
Any WYSIWYG editor
You use it to push crap.