Jaimie, there are five viable eye-trackers out there, group by expense:
ERICA by Eyeresponse (Eyeresponse.com): Smallest, portable, most affordable, good infrared controls, good battery, powerful and upgradable tablet Windows OS, yet weak on ambient light interference and eye issues, uses easy to follow "Lifemate" software for building communication and control boards, user must face unit head-on for accuracy, camera is external, ($7-9000) made in the US
Eyegaze Edge by LC Technologies (Eyegaze.com): Most accurate in all lighting and eye conditions, powerful and upgradable portable tablet or customized desktop systems (Mac base with Windows XP), uses easy to follow "Eyegaze" software for building communication and control boards (yet can also use all competitors' software programs as well if preferred - Viking, The Grid, Speaking Dynamically), user can look at screen from any angle including sideways, camera is external and can be attached to any firewire computer ($8000-10,500), made in US
Tobii by Tobii/ATI (Tobii.com): Biggest screen (yet heaviest unit), most cameras built-in which allows for greater head movement accommodation, uses easy to use "Viking" software for building communication and control boards, in-house manufactured tablet that cannot be upgraded, not portable unless external wheelchair connection or power inverter used, user must face unit head-on with no angles, cameras are internal ($13-15,000), made in Sweden
Eyemax by Dynavox (Dynavox.com): Most famous company for AAC (communication), yet uses the weakest of the four cameras (known as a "Quickglance") but has the easiest interface which works with their communication software as well, accuracy good but weak on eye issues and some eye-glasses, heavy unit, in-house design so upgrades are difficult, portable design using Windows XP, user must face unit head-on with no angles, ($14-16,000), made in US
Prentke Romich (prentrom.com): Famous AAC company is coming out with a unit as well, using Tobii's camera. No info at this time.