$ sudo apt-get install arduino
After installed, you can start Arduino IDE from Start menu of Raspberry Pi desktop > Electronics > Arduino IDE.
Or enter the command in Terminal:
The install version is 1.0.1.
Cross post with Arduino-er.
Updated@2013-12-13: more details to Learn how to install the Arduino IDE on your Raspberry Pi so that you can write and upload programs onto an Arduino.
There is a thread on the Pi forum discussing installation of later versions of the Arduino IDE: Arduino_IDE-1.6.7/github on the Raspberry Pi