AirPort: Apple Computer's 802.11b (currently - could change in future?) that is standard 1-2-5.5-11 Megabit transmission over the 2.4Ghz frequency spectrum. Depending on which country you live in, it can use up to 13 (11 in the US) channels - akin to CD radio channels, though none are reserved for the police :-).
The sell a BaseStation for about $300 - which includes a 56k modem, a KarlNet based 486 PC with 4 MB memory (flashable), and a Lucent/Orinocco/whatever Silver (40/64-bit WEP encryption). The BaseStation is an AccessPoint - and a hackable one at that!
You can add a different 802.11b (other PC-Card? g? a?) card for more encryption ("Gold" -> 128-bit WEP)
- You can add a Lucent external antenna to increase the range, or any other 2.4 GHz antenna that has a Lucent plug
The AirPort client cards sell for about $100 from Apple, and fit in any modern Mac CPU - G4 Towers, iMacDV's (400 MHz or newer), any iBook, newer G3 PowerBook and any G4 PowerBook.
They've got a pretty detailed consumer-level description at: http://www.apple.com/airport
Modifications for the Base Station can be found at: http://www.vonwentzel.net/ABS/ ---
N.B. The above refers to Apple's AirPort Base Station v1, aka "Graphite" for its color scheme. Apple released a new version of the AirPort, v2, commonly referred to as the "Snow" base station because of its white case. Snow base stations are completely different from the original graphites -- instead of 486s running KarlNet, they are some kind of PPC implementation. Little is known about their firmware, and they are not (yet) hackable. It <i>is</i> easier to add an antenna to a Snow BS (less case mangling required).