A driver for Atheros AR5000-series 54Mbps 802.11g wireless PCI cards has been released for AmigaOS 4. It supports WPA/WPA2 encryption (as well as WEP), and is available for free on Aminet. PCI-Express cards may also work but are untested.
Versions of the driver are already distributed with AROS and MorphOS, but it is unlikely to become available for AmigaOS 3 because of DMA requirements.
I guess the number of possible users would be pretty low, but... Wouldn't it work on classics with g-rex?