Large scale WiFi deployment
Setting up large wifi networks for campusses or outdoor is quite a challenge.
hardware
The hardware allows different functionalities. Generally you need AP's (Access Points), maybe repeaters and a management system. AP's have a maximum amount of concurrent / simultaneous users.
Cisco Enterprise Wifi - Enterprise APs have a max of 24 simultaneous users, making this expensive and useless for large deployments
Netgear - has bugs with wireless N. Don't use!
Ruckus - highly recommended
Ubiquiti - new and in heavy development. A bit experimental but promising
management and billing
For management and billing you have several options, which include determining who your users are, printing vouchers, walled gardens, being able to change the default page, filtering by MAC address, etc. Most couple with a radius server.
CoovaChilli Free
HotSpotEngine Cheap
Hotspot Express Hotex billing manager
Patronsoft Firstspot Heavily developed but Windows based
Aradial Linux based and heavily developed
meshing
This is the technology that allows APs to communicate with the controller wirelessly instead of having to run cat-5 cables from a switch to each AP