Lambda the Ultimate

D3 is a popular HTML5 visualization framework. While similar to other JS frameworks in its exposure of CSS/SVG, its enter()/exit() abstraction is an elegant leap for structuring code. Check out Mike Bostock's short and direct explanation Thinking with Joins:

Say you’re making a basic scatterplot using D3, and you need to create some SVG circle elements to visualize your data. You may be surprised to discover that D3 has no primitive for creating multiple DOM elements. WAT?

I particularly appreciated the practicality of this model for designing animated transitions. You can also check out the beautiful gallery of examples.