Microsoft have just released Internet Explorer 8 Beta 1! You can download it from here.
Seems solid so far, you can tell it to Emulate IE7 if you need a website that won't work correctly in IE8 at the moment. As IE8 will now be using standards mode by default it'll probably effect a great many websites (even the back end of the blogs here doesn't work properly in standards mode IE8), so they'll need to be updated, or use the following to tell IE8 to render in IE7 mode:
meta http-equiv="X-UA-Compatible" content="IE=7" /
Which must be placed at the top of the head of the document.
A few new features too, one I'm looking into is WebSlices, which are sort of like RSS Feeds, I'll see if I can put together something on the forums that will make use of them.
I'll probably be posting up more thoughts over the next few days, I'd recommend everybody who toys with any web development to start using this ASAP and updating their websites so by the time it goes final the whole world won't break from IE behaving in a more standards-compliant way.