In the Arduino/Pi circle the MCP2515 and MCP2551 are widely used, they connect using SPI, you can get them as individual modules which are much cheaper or a shield like this.
This PiCAN 2 board provide CAN-Bus capability for the Raspberry Pi. It uses the Microchip MCP2515 CAN controller with MCP2551 CAN transceiver. Connection are made via DB9 or 3 way screw terminal. Easy to install SocketCAN driver. Programming can be done in C or Python. Features CAN v2.0B at 1...
www.elektor.com
You can use an analyzer to read the data on the bus, I use this little guy for I2C and I believe it works with CAN as well.
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If not this does for sure.
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For a couple years now I've been eyeing up CAN, I fell in love when I first read about it, sounds to good to be true. A few weeks ago I actually ordered 3 modules to mess with but haven't gotten to them yet. I found these cool boards which are perfect for prototyping as they have the ATmega32u4 (Arduino Leonardo) embedded so just need to program the boards, connect and play. I got a great deal too at $14.90 each.
CANBed - Arduino CAN-BUS Development Kit carries an Microchip ATmega32U4 chip and MCP2515, MCP2551 CAN-BUS controller and transceiver to realize the CAN-BUS communication protocol on a single board without other MCU to control, it is a CAN-BUS Development Board itself!
www.seeedstudio.com