When it comes to free admin utilities, BGInfo is one of my favorites. It's small. It doesn't take a lot of resources. And did I mention that it was free? Scott Lowe recently did a tip on BGInfo in TechRepublic's Windows Server 2003 newsletter, which refreshed my memory about this great little tool that puts system info (server name, domain, IP address, and lots of other options) in text on the wallpaper of a Windows server. This is especially helpful when you manage a bunch of servers and/or you often switch between multiple servers over KVM. A glance at the system info can keep you from making a configuration change to the wrong machine.
I used to have BGInfo on several different servers, but I hadn't thought about using it for a while. After reading Scott's tip I went and put BGInfo on a bunch of different systems. Judging by the discussion to Scott's tip, I wasn't the only one. The discussion also talks about the best ways to automatically deploy this across multiple servers.
For screen shots of BGInfo, take a look at this article.