Harry Potter and the Half-Blood Prince by JK Rowling will be available by July 16. But in case you want to find out more about the book before then, you may want to visit Rowling's official website. It's an interactive site, so your computer better have a good connection, high-resolution, speakers, etc.
You'll need to explore the page by pointing your mouse at the objects on the page to see what's available. But if you don't like playing games (are you sure you're a Harry Potter fan?) or just don't have the time or bandwidth, check out the text-only version. And no, it's not just a public relations site. Rowling actually talks about herself, how she writes and the nasty rumors about her.
And for the blogging addicts out there who want to leave comments, the official website won't allow you to do that. But there is a blog that you can visit—The Leaky Cauldron, which Rowling herself visits and on which she has bestowed a Fan Site Award. One of its founders will even be interviewing Rowling on the day of the launch of Book 6. Right now, commenting on the blog posts has been disabled because of the tremendous amount of traffic the blog is getting, but you can participate in the forums at Leaky Lounge.