An UNO and Ethernet shield like below should get you started with your projects.
http://www.ebay.com/itm/1x-Ethernet-Shield-W5100-For-Arduino-Main-Board-2009-UNO-ATMega328-1280-MEGA2560-/261425719620?pt=LH_DefaultDomain_0&hash=item3cde2fe944
http://www.ebay.com/itm/Version-Board-ATmega328P-UNO-R3-ATmega16U2-Free-USB-Cable-for-Arduino-TE-/121278847597?pt=LH_DefaultDomain_2&hash=item1c3cc85a6d