Official Microsoft Compatibility Center

[Skaughtto]

Windows Compatibility Center: Find Updates, Drivers, & Downloads for Windows 8, Windows RT and Windows 7

All of the Lumia WP7 Lumias have a big red X under the RT tab...

There are a couple USB to Ethernet adapters that say they are compatible though:
Cisco USB Ethernet Adapter USB300M
Netgear FA101 USB Ethernet Adapter
Netgear PA101 USB Ethernet Adapter (Phone Line?)

 

[mcheiron]

According to MS my Canon pixma 4300 is compatible, but it actually is not, as confirmed by Canon's support, like many other older Canon inkjet usb printers.

 

[Skaughtto]

Yeah, I tried a PS3 controller... it detected and RT knew what it was, but no games used it.

 

[kashk5]

According to the site, there are A LOT of USB to Ethernet adapters that are compatible. With one of these, my Surface is officially a laptop replacement.