The very versatile 3com Etherlink 3 (III) 3c509b This card is a great go to as it works in both 8bit and 16bit isa slots There is a modified software on GitHub to allow it to run in an XT machine and runs natively in an AT machine These are great little 10mb cards and versatile as has multiple interface options. BNC, AUI and RJ45 what we all know as the standard Ethernet Allows you to easily get online with an XT or AT and can use the packet drivers under DOS with MTCP and even Microweb for a Browser - I know as I use these cards in all my XT and AT class machines. Can provide links post purchase (eBay doesn’t allow it)
eBay