I've always liked the idea of the Raspberry Pi.
Although I'm struggling to find ideas for one.
I used to have a small cluster of Dell and Cobalt servers doing various things, and a while back I consolidated into one HP MicroServer.
Since then I've found it difficult to justify having another server, albeit a small low-power server, running to do anything.
The one thing that does interest me is scriptable Minecraft. I tend to play that a lot, and the ability to fairly simply generate levels with a simple API is quite appealing.