Whoa, thanks for the replies!
To answer some questions: I was thinking of going for a mini-itx and a smaller case mostly because I live in an apartment and generally have less room. That said, I could still go larger in terms of motherboard and case. The 8GB of RAM is overkill; however, because of RAM prices I was thinking of going for 2x4GB, and just using 4GB to start.
So, it sounds like a little higher pico psu (120-150W maybe) paired with a near equivalent brick might be good.
Though I'm new at constructing a server, what HFat said about maybe going with a CPU with more cores (more threads) and then underclocking it makes sense to me. I was looking at desktop quad-core processors, it seems like the cheapest are AMD, such as the AMD Phenom II X4 840
(95W TDP) (there are also older, cheaper versions). Also, while everyone said that Intel boards are most efficient, I'm guessing that there are some simple motherboards that will come close (as I don't need many features on the board).
Also, in terms of usage, it will probably be small, as I will be mainly hosting personal projects/sites running PHP and mysql. However, I was hoping to make a system that I will have for a while and be flexible to increased usage.