I've been looking over the HTML5 drafts and HTML4 - HTML5 differences doc, and here's a list of bits that caught my eye, and why.
textarea now supports
wrap again. This is cool if you've got a text box that takes code listings (which I do).
input element supports: datetime|datetime-local|date|month|week|time|number|range|email|url - perfect for validation.
manifest attribute, lending more support to offline (web) apps.
strike tag is being binned. The funny thing being all the blogs that use the tag to indicate a correction will, without an update (and if they're in standards mode), have the mistake plugged back in. Then again, the browsers will probably keep the tag.
name attribute is being striped away from forms and the like (obviously not inputs elements). No more excuses IE.
getElementsByClassName. Need I say more?
classList. We will be able to use methods such as
toggle() to manipulate classes on elements. I can almost smell the library changes.