Wi-Fi Alliance

Wi-Fi (for "wireless fidelity") is the term for a high-frequency wireless local area network (WLAN).
The Institute of Electrical and Electronics Engineers (IEEE) has specified WiFi and it is part of a series of wireless specifications.

IEEE Standards

The Wi-Fi options available:

802.11B
802.11B is the oldest established Wi-Fi technology. 802.11B operates in the 2.4 GHz frequency range. Advantages are low prices and compatibility. An 802.11B network supports data rates of up to 11 Mbps. In reality it works mostly only up to 5 or 6 Mbps. The disadvantage is the lower security and performance. Numerous hacking tools, designed specifically for exploiting 802.11B networks, are around. Because of the operating frequency band of 2.4 GHz, it is susceptible to interference from microwave ovens and 2.4 GHz cordless phones.

802.11G
802.11G is an extension to 802.11B and operates also in the 2.4 GHz frequency range. 802.11G works at data rates up to 54 Mbps. The entire 802.11G frequency range consists of 90 MHz of total bandwidth. Each access point requires 30 MHz of bandwidth and only three access points are possible in a certain area. The 802.11G signal also has a shorter range than an 802.11B signal. All 802.11G devices are backward compatible with 802.11B devices. Upgrading an 802.11B system to 802.11G is painless.

802.11A
Completely different from 802.11B and 802.11G, the 802.11A works at a data rate of 54 Mbps. Multiple channels can be combined for higher data rates. The 802.11A specification provides 12 non-overlapping channels in the 5.8 GHz range. 12 access points can work in the same area using these 12 channels. By combining channels (the so called turbo mode) less access points are possible.
Because of the operating range of 5.8 GHz and only a few devices working in this range (at this time), 802.11A is much more safe concerning interference from other devices.

802.11G or 802.11A are the choices of today. Using 802.11B, the upgrade is easy to 802.11G. For a new system, using 802.11A should be considered.