The Thunderbolt port on the MacBook Airs supports one external display. You can use that with a Mini DisplayPort to Dual-Link DVI adapter to run a 30" screen (2560x1600). @andynormancx mentioned DisplayLink adapters and that some can do 2048x1152; the Air has 2 USB ports, so let's say that you can run two of that size of monitor with them (you may be able to squeeze more in there). Finally, there's the internal display (the 11" has 1366x768; if you want bigger, the 13" is 1440x900).
In total, you're looking at 2560*1600 + (2048*1152)*2 + 1366*768 = 9,863,680 pixels. Is that big enough?