TI MSP430 Launchpad + Ethernet
The Arduino Ethernet shield is built around the Wiznet W5100. The chip provides a complete TCP/IP stack and can ethernet.

Porting the Arduino driver code to the Launchpad should be fairly straightforward, you'll need SPI and a few control lines.

http://code.google.com/p/arduino/source/browse/trunk/libraries/Ethernet/utility/w5100.cpp

Here's some Launchpad SPI code of mine to get you started:

http://blog.hodgepig.org/2010/09/10/575/

The Launchpad currently has no official shield standard though there are efforts afoot:

http://www.43oh.com/forum/viewtopic.php?f=19&amp;t=16&amp;start=10

http://www.msp430launchpad.com/2010/08/shield-standard-proposal.html