CSS

Cascading Style Sheets (aka "CSS") is crazy nutty stuff that is slowly starting to make me forget to shower each day and wander the streets of New York City, babbling about clearing floats (yes, of course I'm kidding about the babbling part).

It never ceases to amaze me what one can accomplish with CSS. One of these days, I must find Mr. Håkon Wium Lie, and shake his hand because the whole concept of CSS is awesome. While it can be a bear to wrestle with at times, I find that the more you "think CSS", the easier it is to let CSS do all the work for you. I believe that the key is to write your clean semantic markup once, and try to leave it alone. After that, planning your layout with good ol' pencil and paper usually means less frustration.

CSS3

CSS3 is a bit of a game changer: there is a whole new level of power with which you can wield your mighty selectors. No more graphics for rounded corners and background images can actually behave the way you want them to. With CSS Transforms / Transitions / Animations, you can rely less on Flash or JavaScript, which keeps pages lighter. Of course not every browser supports every life-altering CSS3 feature, but we are getting there slowly but surely (and of course with good planning, graceful degradation allows us to make the user experience for those with dusty browsers as pleasant as possible).