How To Integrate/aggregate 2 Or More WordPress Blogs In To A Master Blog?

Well I have more than one wordpress blog and all deal in different topics but I want the content or the posts to appear on a single blog which may be the master blog of all. Like I update blog3 then its post should appear on the master blog and when clicked on it, it should go to the original post page on blog 3. Practical example of this is Gigaom.com. They have aggregated almost 6 blogs(TheAppleBlog,Earth2Tech etc.) into a single master blog that is Gigaom.com.