Microsoft has a great gem of a product for small business that's basically "under the radar" - Windows Home Server.
Although it's called a "home" server, it's also great for small businesses. Users can centrally store files, backup of workstations on the network occurs automatically (so you don't have to worry about your employees remembering to backup), and files can be accessed remotely. This is a perfect fit for smaller offices - a few users who need to collaborate, and don't have the need or budget for a full-blown server.
About a week ago, Steve Ballmer announced that Microsoft was planning to remove an imporant feature (drive extender) from the next release. Although Microsoft is now indicating they'll revisit this decision, yesterday more bad news came out with HP announcing they were going to drop the product line: http://yhoo.it/f8Noo7.
Windows Home Server is a product we have highly recommended to several of our small business clients who we provide IT support to. Although Microsoft has promotional information on their web site for small business, it really hasn't been marketed to its full potential. We don't want to see this go away!