If you go for the Samsung 840 and are mounting it into a desktop or a notebook with a 9.5mm hdd height, I'd recommend the kit rather than the standalone drive if you are buying them at full price. The kit comes with a USB to Sata adapter, a 2.5 inch to 3.5 mounting brace, a sata cable, screws to hold it all in place, and a hdd spacer for hdd bays in non-ultrabooks (9.5mm) for $10 more than the standalone drive. That being said, you will be more likely to find sales on the standalone drive and the stand-alone drive should fit ultrabooks (7mm) just fine. Just be aware that you may need additional mounting hardware if you go with the stand-alone drive.
Samsung 840 with installation kit...