I have been playing with a Dlink DFE580TX quad ethernet card. I have used it in both 2.4.x and 2.2.19 kernels and it works a treat. We have got a batch of them at work, and they are now down to a price where they are affordable for the largish home network. Mind you, 4 single cards are still cheaper than one quad, but you save 3 PCI slots.

You have to get the latest 'sundance' drivers from http://www.scyld.com/network/sundance.html. Don't use the one with the 2.4 kernel tree.