Besides Ethernet, Arcnet is the second networking type that works on broadcast mediums. The arcnet card supported is the Commodore A2060. Please pay attention that you get it with the 'right' driver hybrid chip, they are available with high impedance (SMD 9058) and low impedance (SMC 9068), according to whether the network card is used in a bus or star topology network. Please see http://cs.uni-bonn.de/info5/system/arcnet.html for a detailled description.
The only arcnet-card supported by NetBSD/amiga right now is the Commodore A2060.