As has been mentioned, you can't daisy-chain multiple Thunderbolt displays to an Air. Two possible add-ons that'll allow you to connect an additional external display:

• Matrox DualHead2Go (in action hooked up to an 11" Air)
• DisplayLink adapter

I've used the latter and they work pretty well for non-intensive applications.

As has been mentioned, you couldn't daisy-chain multiple Thunderbolt displays on pre-2012 Airs. Two possible add-ons that'll allow you to connect an additional external display:

• Matrox DualHead2Go (in action hooked up to an 11" Air)
• DisplayLink adapter

I've used the latter and they work pretty well for non-intensive applications.