Admittedly this is a little premature, but I'm keen to detach my printer from the host computer as soon as possible. Wired Ethernet is my preferred option - it can be accessed from all of my devices (desktops, laptops, iPad, iPhone, etc), is fast, reliable and fairly cheap compared with wireless options.
Reading this tutorial Arduino Ethernet + SD makes it sound doable and there's a chance I can borrow an Ethernet shield to have a play.
I envisage an Aduino/Ethernet combo acting as the host and talking serial to the printer's Arduino Mega/RAMPS controller. The host would support uploading a G-code file to the SD card, queuing prints, control power to the printer (toggle ATX power) and also act as a watchdog by monitoring printer enclosure temperature/dead comms link. Cost of the Ethernet module would be somewhat offset by avoiding the need for a display/controls on the host/printer as these can be provided via the web interface and accessed from a existing device.
It might also be practical for the host to operate multiple printers - something I'm keen to try.