Is there another Arduino ethernet module besides the “Arduino Ethernet Shield”?

There is also one from Freetronics, which works with Arduino and I have also tested it with Netduino. You can also get a nice PoE adapter from them. Their shield is also based on the Wiznet 5100 chip, and has incorporated the following design features to hopefully help with any issues with the Arduino Ethernet Shield (taken from their website)

SPI Fixes

Combining Ethernet with other SPI devices can be really tricky because the Wiznet chip doesn't relinquish the bus properly when it's deselected. To fix that problem we slaved the Wiznet's SEN (SPI Enable) line to the CS (Chip Select) line, which means that whenever your sketch deselects the Ethernet connection in order to talk to another SPI device it will work exactly the way it should.

No more messing around with cutting tracks and other nasty hacks you may have seen mentioned on the forums.

Reset Fixes

We've also slaved the Ethernet Shield's reset line to the Arduino reset line, so if your Arduino is reset the Ethernet Shield will automatically reset as well. The Wiznet reset line is also held active for long enough to make it restart reliably each time the Arduino itself restarts.

Power Filtering Fixes

Ethernet connections are very susceptible to electrical noise, so the Wiznet chip has multiple ground pins on two separate buses and they need to be individually decoupled and the buses linked by an inductor. We took care of that by implementing proper decoupling on the power and ground rails, ensuring you get maximum reliability even in electrically noisy environments.

The official is implemented with a Wiznet 5100 chip.

There is another ethernet shield from NueEletronics implemented with the ENC28J60.

I can think of two options off the top of my head:

• An Xport
• A custom solution with an ethernet PHY, a magjack, a SPI connection and a bunch of custom software.