Bought the Patriot EP Series 32GB SDHC as secondary storage.
Patriot Signature EP Series Flash 32GB SDHC Flash Memory Card Class 10
Fast speeds with the built-in card reader on the 2012 MBA. 28MB/s write, 37MB/s read. It's probably even faster with a dedicated card reader.
Perfect for storing my movie downloads. 720p videos load without delay with VLC.
Would recommend it for anyone looking for a minor space increase that's cheap, fast, and portable. However, it does stick out as all SD cards do. If you're looking for something flush, the Nifty MiniDrive comes out later this year.