Windows Live Academic
Microsoft has developed some competition for Google Scholar: Windows Live Academic. Currently in beta, this service only covers physics, engineering and computer science. In my opinion, it is a better service than Google Scholar, but still does not meet the needs of those doing very comprehensive research.
However, the advantages are on target. A split screen allows the user to scroll through the results list on the left side, mouse over an interesting article, and preview that article in the right side of the screen. This prevents a lot of "linking out" of the results list. Also, there is the option to create RSS feeds for specific topics or authors, so you can be alerted when a new item comes online.
Reviews on the product are available here, here, and here.
Below, some of the explanatory text on the Windows Live Academic home page: