How can I make my 27" iMac and my 27" Thunderbolt display the same height?
I'd recommend buying this book: 

http://www.amazon.com/Life-Times-Thunderbolt-Kid-Memoir/dp/0767919378/ref=sr_1_7?ie=UTF8&amp;qid=1330596630&amp;sr=8-7

It's exactly 1" thick, put it under the monitor.