New thunderbolt MacBook Air and external monitors
They're the same as for other computers with Thunderbolt:


DVI/VGA/HDMI with cheap passive Mini DisplayPort adapters (audio is included over HDMI, assuming your adapter supports it)
dual-link DVI with a more-expensive active Mini DisplayPort adapter
any native DisplayPort monitor (many mid-to-high-end monitors already have them)
any Thunderbolt monitor (all one of them currently announced)


You can use any Mini DisplayPort adapter that you might already have, or any that are available for purchase. I have my brand-new 2011 MBA hooked up with a Monoprice MDP->DVI adapter right now.