Internet Explorer Beta 2 released last week (downloads).
Here is the current list of companies providing new accelerators, web slices, and search providers. It's an impressive list, and we expect other big names forthcoming.
There is also a Videos site (overview, accelerators, web slices, and security and reliability enhancements).
To give one a sense of the enhancements, consider these blog posts. I've added the features that the posts describe. Just looking across this list, you'll see that IE8 intends to be the leader, not just a contender:
Other interesting facts: