pfSense includes built in wireless capabilities that allow you to turn your pfSense install into a wireless access point, use a wireless 802.11 connection as a WAN connection, or both.
There are a variety of wireless cards supported in FreeBSD 7.0, and pfSense includes support for every card supported by FreeBSD. Some are supported better than others. Most pfSense developers work with Atheros hardware, so it tends to be the most recommended hardware. Many have success with other cards as well.
Linksys, D-Link, Netgear and other major manufacturers commonly change the chipsets used in their wireless cards without changing the model number. There is no way to ensure a specific model card from these vendors will be compatible because you have no way of knowing which "minor" card revision you will end up with. While one revision of a particular model may be compatible and work well, another card of the same model may be incompatible. For this reason, we recommend avoiding cards from the major manufacturers. If you have one on hand, it's worth trying to see if it is compatible, but be warned if you purchase one because the "same" model worked for someone else, you may end up with a completely different piece of hardware that is incompatible.
The following drivers are included in the pfSense 1.2.1 and newer kernels.
Supports cards based on the Atheros AR5210, AR5211 and AR5212 chipsets. This includes a wide variety of wireless cards. The following are known to work in pfSense, though there are also many additional options.
Ralink Technology IEEE 802.11 wireless network driver - supports cards based on the Ralink Technology RT2500, RT2501 and RT2600 chipsets.
Lucent Hermes, Intersil PRISM and Spectrum24 IEEE 802.11 driver - supports cards based on Lucent Hermes, Intersil PRISM-II, Intersil PRISM-2.5, Intersil Prism-3, and Symbol Spectrum24 chipsets. These cards support only 802.11b.
Aironet Communications 4500/4800 wireless network adapter driver - supports Aironet Communications 4500 and 4800 wireless network adapters and variants.
AMD PCnetMobile IEEE 802.11 PCMCIA wireless network driver - supports cards based on the AMD 79c930 controller with Intersil (formerly Harris) PRISM radio chipset.
Here is a spreadsheet with a compatibility matrix and driver list for cards that should work with 2.0 - be aware of the "hostap" column, which shows which drivers are capable of running in access point mode. If that column is marked N, then the card could only be used as a client.
The second tab on the sheet lists part numbers for a given driver.
This information was compiled from FreeBSD man pages and driver source code, and some from submitted information/experience.