Where can I find a better pinout diagram for "Arduino Ethernet" board?
The formal Arduino.cc website mentions, somewhat obscurely, that the Arduino Ethernet is pin compatible with Arduino Uno:


  The Revision 3 of the board introduces the standardized 1.0 pinout


Except for pins 10-13:


  Pins 10, 11, 12 and 13 are reserved for interfacing with the Ethernet
  module and should not be used otherwise. This reduces the number of
  available pins to 9, with 4 available as PWM outputs.


The other difference is the onboard LED is connected to pin 9 rather than the Uno's pin 13:


  On most other arduino boards, this LED is found on pin 13. It is on pin 9 on the Ethernet board because pin 13 is used as part of the SPI connection.


You can use any Arduino Uno pinout diagram as a reference, the one you have found seems to be pretty elaborated.