I found out that using the Arduino Ehternet together with a lot of shields out there, gives you problems. Most pins you need for your shield, are in use by the ethernet ans SD. But still you want to have ethernet AND SD for your project.
I'm might have found a workaround.
Will working with the sure32x8 LED matrix boards, I found out SRAM runs out very quickly, so I decided to have make a barebone Arduino that controls the sure32x8 LED matrix boards and get's it's buffer (for showing text) filled by the Arduino Ethernet over I2C. It works very good this way.
So I started thinking one could do the same thing for using all those shields out there. You just connect your shield to your barbone arduino and you just send triggers from your Arduino Shield over I2C.
For know I just made this on a breadboard, but I'm planning to make an BARBONE SHIELD (with ATMEGA328P) you can plug onto your Arduino Ethernet. My breadboard example costs about € 7,5 (without the breadboard).
The shield to make, would actually only need 4 pins: GND, +5V, A4, A5
someone else interested in this set up?