Yep - it's not cheap, but you'll get a seamless easy connect monitor with decent built in speakers. If you have the $1200+ to spend to begin with, you could also get a current model iMac 21 and get two computers out of the deal (although you'd still need an extra keyboard and trackpad, and the the TB cable) if you want to run the air in clamshell mode.
When I have some extra money, I plan on getting a TB monitor myself, so that when I'm in the office, I can have all my spreadsheets and files open and usable at once without constantly digging for which sheet I need.