Does the 802.3 Ethernet standard provide a recommended circuit design?
IEEE802.3 is thousands of pages covering everything from 1 Mb/s to 100 Gb/s systems. You can download and read the standard for yourself here.

IEEE provides little in the way of reference implementations. However the chipmakers who provide the PHY devices will typically provide reference designs. These designs will, however, depend on you to provide a uC implementing all the higher layers of the ethernet stack (from the MAC on up).