AWOL,
Thanks for the comments!
dewyoder18,
I purchased the housing from SparkFun (it's called the Arduino Project Enclosure). It seems designed to fit an Arduino, battery, and Ethernet shield (with a little plastic removable tab for the Ethernet port). In practice I found that the space for the battery was perfect for my circuit, and the space for the Ethernet Shield was just enough space for some panel-mount jacks and the LCD screen.
It's a bit on the small side, so it's a little cramped in there. But it works!