There are many different network cards. Each one has specific documentation.
3com 90x, 90xB, 90xC are PCI ethernet adapters which provide full bus-master operation, download/upload packet chains. All of them allow auto-negotiation. 90xB and 90xC have power management capabilities. Many 3com cards share the programming interface with these models, an example is the 3c556 10/100 LAN + 56k Modem MiniPCI adapter, 3c555 10/100 LAN MiniPCI.
The Ne2000 network card chipset was a reference design that was never meant to go into mainstream production, but after Novell used it as cheap hardware to go with their software it became popular. It is a good first network card to program because it follows a simple design (making it helpful for learning), they're probably dirt-cheap, and it is supported by most PC emulators. Both Bochs and QEMU provide ISA and PCI implementations.
Ne2000 is not technically a card, it is a standard that several implementers follow. The best available description of the initial standard is located DP8390D/NS32490D NIC Network Interface Controller and was published by National Semiconductor.
The RTL8139 Network Chip is used on many old Ethernet Network Devices. It supports 10 and 100 MBit.
The RTL8169 is Realtek's next generation of high-performance network cards. This particular chipset is designed to operate at 10/100/1000 Mbps speeds.