The Taiwan-based chipmaker Ralink may be the solution for many users of Mac OS X 10.4 Tiger trying to find a Wi-Fi adapter that works with their particular machine. Although few companies make Wi-Fi products that include or support Tiger drivers, several companies use chips from Broadcom, Apple's Wi-Fi chip supplier, which enables their products to work on a Mac without additional software.
However, Broadcom's competitors have made inroads into the Wi-Fi market, and some products that worked six months ago - for instance, a Belkin 802.11g PCI Card - have been re-engineered to save costs and no longer use Broadcom chips. Manufacturers rarely directly disclose which chips are in which products to avoid making promises about the underlying technology; they're promising functionality (i.e., a Wi-Fi connection).
That's what makes Ralink's unsupported drivers for Mac OS X 10.2 through 10.4 and Linux so interesting: if you wind up with a Ralink-based device, you can still use it with your Mac. Ralink has been listening to its indirect Mac customers, because they recently updated their drivers for Mac OS X 10.4 Tiger, and they seem to release regular bug fix updates as well.
Ralink's driver page contains downloads for supported products, but it's organized by internal chipset and product names. I hope some enterprising soul will figure out which products and versions from major makers use Ralink chips, expanding Mac users' options.
Belkin's 802.11g PCI Card (part number F5D7000) claims to have Mac OS X 10.2 and 10.3 (not 10.4) compatibility on its detail page, but doesn't offer drivers for download via the linked page. Al Varnell wrote in point out that you must take a different route to find drivers by visiting Belkin's download section and navigating to the product. I have no idea why the drivers aren't properly linked in both directions! The drivers were updated in April, 2005 and include no mention of Tiger compatibility. (Belkin also has Panther drivers for other products.)
There are now Tiger-supported USB 2.0 adapters for Macs - I found this out almost by accident. The ZyXEL AG-225H, a Wi-Fi hotspot detector with a built-in LCD screen, doubles as an 802.11a/b/g adapter using USB 2.0. ZyXEL provides Mac drivers for both Panther and Tiger; I haven't tested them but have been told that they work by other Mac users. I reviewed the ZyXEL unit, looking primarily at its Wi-Fi finding functions, for Mobile Pipeline back in September, 2005. It's about $75 from several online retailers.
Thanks to Dave Goldman for this tip!