There are various modules on the market for connecting devices to ethernet LANs.
Some are Arduino-specific, i.e. the shield from Sparkfun, DEV-09026, $46.
Others seem to be "generic", and connect (on the device-to-connect-to-LAN side) via a serial interface. (Are there other options?). The Sparkfun /WIZnet Serial-to-Ethernet Gateway looks distinctly cool, especially at $30, complete with built in webserver.
Pros and cons? I always prefer a simple, general answer. I use ModernDevice RBBBs, anyway, so a shield's easy "plug in", the easy management of the physical problems of connection are not going to help me, anyway, are they?
Are there other advantages to a shield that I'm missing?
What should I look for in an Arduino to LAN module?
I don't mind having to configure the module "the hard way", i.e. by connecting it up to a big PC and setting a fixed IP address, etc.