Lazy and conditional image loading with a CSS placeholder and loading animation.
Adds tab content behaviour with associated ARIA roles and hints.
Simple, jQuery nestable click-to-open dropdown menu. Supports touch.
Tidy little CSS hover tooltips, no JS required.
A touch-enabled jQuery dropdown menu with hover intent for mouse events.
I used to always use this technique but I kind of like the native ones. Re-jigged and inspired for 2011 by http://jsfiddle.net/mnjKX/16/