B&H is offering up to 31% off PNY StorEDGE flash memory expansion for MacBooks : 128GB $98, 64GB $52 with free shipping. These cards are designed to live inside a MacBook Air/Pro or Retina and provide a handy additional 128GB or 64GB of space. The shortened size means they are flush with the sides of the MacBook and won’t protrude out. Rated 4 stars on Amazon.
Update: BACK IN STOCK! Amazon has the 64GB StorEDGE available for $39.99 with free shipping.