The Arduino enclosure allows you to easily enclose your Arduino main board, Arduino Mega, or any other board that fits the Arduino foot print (FEZ Domino, FEZ Panda, Netduino, etc). It simply presses shut, so you don't have to worry about screws or fasteners.
It has room internally for an Arduino and a shield. It even has a removable tab mated for use with an Ethernet shield. It also has a snap-in compartment in the back for accessing switches or connections or battery access.
Note: Some older Arduino boards have a slightly smaller hole near the rear the ICSP connector. To make the case work with these boards simply drill out the hole to 1/8" and you will be fine. Also, with the newer Ethernet Shields, you will need to remove one of the pegs to get everything to fit correctly.