Some Intel 10/100/1000bT NICs work as early as OS X 10.2. I use one in my beige G3. Doesn't work in OS 9, though.

Actually, your Matrox cards may have had Mac counterparts. Many of the Matrox-branded Millenium and Millenium II cards can be flashed to work on a Mac, but some of the OEM versions have too small of a Flash/EEPROM chip to be able to fit the whole Mac ROM, so they won't work.