Trancend Jetdrive, 128gb storage. Basically a shortened SD card so that it ends up flush with the case of a Macbook Air or Macbook Pro.
Obviously won't be as fast as your internal SSD, but handy if you've got a measly internal amount like me and you want to move your photos/itunes to free up space.
There are 3 versions, all "Max read: 95 MBps, max write: 60 MBps"
Transcend JetDrive Lite 130 128GB Storage Expansion Card
For Macbook Air 13-inch (late 2010 - mid 2013)
(The one in the direct link)
Transcend JetDrive Lite 350 128GB Storage Expansion Card
For Macbook Pro with Retina display 15-inch (mid 2012 - early 2013)http://www.amazon.co.uk/gp/product/B00K73NT1C/ref=pe_186441_50490981_em_1p_1_ti
Transcend JetDrive Lite 360 128GB Storage Expansion Card
For Macbook Pro with Retina display 15-inch (late 2013)http://www.amazon.co.uk/gp/product/B00K73NWK0/ref=pe_186441_50490981_em_1p_2_ti
There's a PNY model, about £80 on Amazon, so be interested to know if anyone has a comparison with the two. This price is about the same as getting it from Amazon.com inc shipping and charges, I believe the PNY could have been had for less but now seems to have gone up to $100.