Available Wireless Protocols
There are a variety of protocols currently in use for wireless networking. Arguably, the most prevalent is 802.11b. Equipment using 802.11b is comparatively inexpensive. The 802.11b wireless communication standard operates in the unregulated 2.4 Ghz frequency range. Unfortunately, so do many other devices such as cordless phones and baby monitors which can interfere with your wireless network traffic. The maximum speed for 802.11b communications is 11 mbps.
The newer 802.11g standard improves on 802.11b. It still uses the same crowded 2.4 Ghz shared by other common household wireless devices, but 802.11g is capable of transmission speeds up to 54 mbps. Equipment designed for 802.11g will still communicate with 802.11b equipment, however mixing the two standards is not generally recommended.
The 802.11a standard is in a whole different frequency range. By broadcasting in the 5 Ghz range 802.11a devices run into a lot less competition and interference from household devices. 802.11a is also capable of transmission speeds up to 54 mbps like the 802.11g standard.
The newest IEEE standard in the Wi-Fi category is 802.11n. It was designed to improve on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one.
The 802.11n standard supports data rates of over 100 Mbps. 802.11n also offers somewhat better range over earlier Wi-Fi standards due to its increased signal intensity. 802.11n equipment is backward compatible with 802.11g gear.
For further detail on wireless protocols and a comparison table, see the Wikipedia page: http://en.wikipedia.org/wiki/IEEE_802.11.