A number of companies are working rapidly to push raw bandwidth in the 2.4 GHz unlicensed radio spectrum to 22 Mbps. A recent FCC decision should accelerate investment and development. The decision is quite technical, but essentially reveals the FCC's willingness to allow use to span a wider variety of practices in that band The full band is 83.5 MHz wide in the US, which means that achieving speeds of over 20 Mbps is well within the constraints of physics.
Two encoding technologies, W-OFDM or Wideband Orthogonal Frequency Division Multiplexing, and PBCC or Packet Binary Convolution Code would both be allowed under both interim and potentially permanent rules for 2.4 GHz. (Full PBCC explanation only in product brochure PDF document).
The IEEE 802.11g working group has been trying to finalize a high-bit rate version of Ethernet that would work in the same space as 802.11b. The March meeting of the working group led to a vote in which OFDM and PBCC were the two remaining contenders, but the IEEE - in a meeting this week - wants to get 75 percent of votes behind one or the other standard before adopting it.
It's unclear how 802.11b and 802.11g would interact, although Texas Instrument has details on a device (PDF link above) that can handle all current 802.11b and 802.11 rates, as well as PBCC, a technology they developed. You can also bet that the IEEE won't promote a technolgy that isn't co-existent with 802.11b as well as Bluetooth. (Read the minutes of the group's March meeting for more details.)
The W-OFDM technology, from Wi-LAN, is the basis for 802.11a radio encoding in the 5 GHz band (see Atheros's approach).
Internetnews.com weighs in with a detailed account, including some of the politics and finances. They identify OFDM's developer as Intersil (the folks who make most 802.11b chipsets), but Wi-LAN's site identifies Wi-LAN as the instigators.
Let's not leave out HomeRF, either: HomeRF 3.0 plans to reach 22 Mbps. However, version 2.0, which hits 10 Mbps, just had its first public demonstrations this last week; 3.0 is not due until next year.