Originally Posted by lavalyn
Software like VMware Server, Microsoft Virtual Server, and Xen are all available for free-as-in-beer, and Xen is open source as well. Plan for virtualization of servers up front for easier scalability, fault-tolerance, and better security through separation of services. Not non-profit specific, of course, but saves money in the mid and long term. But you probably knew that already.
Not only that...but you can get more use out of one box!
It doesnt take powerful hardware to run a sever for most people's needs (tons of exceptions to that, I'm sure) so you might be able to actually run 2 servers on one machine...
Also, to add another one or two to the list, check out these open source routers. Just slap some old network cards in an old PC and load the CD Rom
IPCop and PFsense. I prefer the later by far, but the (community) support is crabby, techy and downright rude sometimes. There's 3 part article on getting IPcop up and running on the link in my sig.