WMM (Wi-Fi Multimedia) aka WME (Wireless Multimedia Extensions)
WMM provides QoS on top of Wi-Fi by adding four data categories each with different time slot lengths. I'm not sure if this is entirely implemented, but the capabilities appear to be there.
IEEE 802.11e (QoS Extension to WLAN) specifies distributed (EDCA) and centralized (HCCA/HCF) schemes for QoS. (See attachment qos11e.pdf for details) Most of the new Atheros cards do support QoS as in WMM which is what EDCA is. The centralized or the point coordinated QoS is not supported by any yet (early 2006).
See, for example the ioctls, wmm, get_wmm, setwmmparams, getwmmparams.