
802.11 a, b, g. The three wireless standards you are probably most familiar with. For quite a while now, there is a new standard in the works that will offer improved speed, coverage, and connection stability. 802.11n is what it is going to be.
The visible or physical change you will see is that routers and adapters will have multiple antennas [commonly 3]. This is the key to the new technology. The standard is aiming to improve the speed, by making simultaneous connections. Range will expand, and stability as well since basically antennas can hand off transmissions to the one with the clearest path. Speed is the most exciting word in this. Wireless will be faster than your 100Mbit connections. I have read rates of 200Mbit, thus double that of wired 100Mbit connections. Of course, with the new CAT6 cabling standard we are up to 1000Mbit (Gigabit) connections, but most places have not upgraded their cabling, routers, switches, and computers yet.
Pre-N hardware has been available to consumers for I don't know how long. But is it wise to spend your money on that? We are warned that since the standard has not been set, it will change, logically. It will be possibly another 6 months before the N-standard is here. Hardware purchased before then may not work well, or at all, when new hardware is produced according to the future industry standard 802.11n.
Even though that risk is real, as I said, manufacturers have already released hardware, and will hopefull continue to support that. I'm guessing that firmware upgrades will allow you to increase the compatibility of your hardware with future standards. If you have the money, need the speed and increased stability now, or are a techy that needs to try the latest, go for it. If you have a currently stable set up, especially for a business environment, then I suggest you hold off.
Check with manufacturers such as Linksys, Netgear, D-Link, and Belkin for pre-N hardware. Keep your eyes open for Wireless-N!