Buffalo WLI-PCI-G54 uses the Broadcom chipset and has a cool-looking external antenna. At this point I think the only hope of getting this to work with Linux would be through Linuxant's driverloader.

D-Link DWL-G520 uses the Atheros 5002 chipset. Should work with the madwifi driver, or with the Linuxant driverloader. It also claims to support 108 Mbps Extreme-G.

Netgear WG311 uses the Intersil Prism GT chipset which has no native Linux driver that I know of. But the Linuxant driverloader says it supports it.

Linksys WMP54G uses the Broadcom chipset and should work with the Linuxant driverloader.

The Linksys WMP55AG is an a/b/g card whereas all the previous were just b/g. This one uses the Atheros 5212a chipset and should work with both the madwifi driver and the Linuxant driverloader. This one is actually just a PCI card with a mini-PCI adapter on it with a mini-PCI card plugged into it.

D-Link DWL-AG520 uses an Atheros chipset and should be supported by both the madwifi and the Linuxant driverloader. Like the Buffalo, it has a nice beefy external antenna.

Netgear WAG311 like the other a/b/g cards is Atheros-based so it should work with both the madwifi and the Linuxant driverloader.
It probably would be a good idea to get an Atheros Super A-G based board so I can go 108Mbps when the drivers support it and when I get a gateway that can go that fast. I don't think my Broadcom-based WRT54G is going to be able to support Super-G. I think the Linksys, D-Link and Netgear a/b/g cards are all based on the same Atheros chipset, so the only deciding factor is likely to be price between these. If anybody has one of these and can inject a bit more data it would be appreciated. I will update and bump this up as I learn more.