A comment pointed me to another version of the Zotac IONITX board that is a bit more expensive, but also has a few more features.
The prices are based on November 24th, 2009.
Case: Apex MI-008 ($39.99) – 250W is a bit overkill. I doubt this system will use more than 60W.
Motherboard/Memory Combo: Zotac IONITX-F-E + [...]