+1 for "home server" and "how low can you go".
How about a "how small can you get it" category?
I would like to see a suggestion for a tiny, quiet and low-power system that still has decent performance. I'm thinking along the lines of i3/i5 with integrated graphics and one of the new mini-ITX boards.
You already have an article on how to get an i5 system to 25W idle/75W max, I would like to see it extended with "nearly silent" fans and the smallest case it could fit into without overheating.
Example uses include
* home server (using NAS or external disks for data storage)
* desktop (without gaming)
* HTPC, for those of us who think that normal HTPC cases are way too big. (A streaming-based HTPC could skip the optical drive.)
The i5-at-25W article uses an i5 661 with overclocked IGP. For a "smallest possible" build I would suggest 660 instead to shave a bit off the peak power, simplifying cooling and possibly allowing a smaller case.
With peak power draw below 70-80 W, an external "brick" type power supply is an option.
"Small" is a feature I am willing to pay a premium for, but not without limits. Perhaps a budget limit of +50% compared to a desktop system of similar performance?