I would stick a nice 100 mbit PCI card in there, some Intel would do fine.
I would recommend against an ISA card. The ISA bus is a big bottleneck, and you'll struggle to even get 10 mbit out of it. Should be fine for a game of Quake though.
But a Pentium Pro is capable of so much more.

DEC Tulip cards are good as well. Ideally you want to genuine article, but clones were available as well that were okay.

jade_angel wrote:

Anything with the Realtek 8139 chipset will be well-supported in Windows (95 through 10, 3.1 may be a little troublesome). The newer gigabit-capable Realtek 8169 and 8111 have Win9x drivers also, but are kinda overkill. But, they're so cheap and common that you might as well.

Intels and 3Coms are better cards, no doubt, and the AMD Lance/PCNet/PCNet-Fast are solid too, but if you want cheap and good enough, Realtek will fit the bill. I would strongly prefer a 3Com (3c905c) or Intel (EEPro100 or EEPro1000) if you're going to be hosting games, though - those chips handle large numbers of packets more adroitly.

Also using Realtek based cards in some of my retro rigs. Since I only use the network connectivity to transfer stuff to and from the rigs, not for network gaming etc, it doesn't matter that they use the CPU for some stuff that more expensive cards does onboard. They're dirt cheap, readily available from retailers, works without any problems whatsoever, and the reference drivers downloaded from Realteks site are small (we're talking kilobytes) and completely free from bloated manager software etc.

You're absolutely right that Intel and 3com cards are better, but not so much better it's worth the extra cost and hassle getting them. If you already got one, use it by all means, but if you have to buy a new NIC, a cheap Realtek one is a great option.