Glyph BlackBox Pro 3TB Drive
If you have one of the new Mac's with USB-C, this drive is the drive for you. It's fast, rugged, and while it does have an external power supply (the one down side), these guys make the best drives out there.
Seagate 2TB USB 3.0
If you're on an iMac or a Macbook Pro with traditional USB 2.0 or 3.0 connections, this drive is affordable, ultra-slim, does not require an external power source, and is my go-to choice for basic users.
This RAID is perfect for video editors, wedding photographers, or anyone with a LOT of data. The USB-C connection means this will be perfect if you have one of the newer Macs to get the best performance.
G-Drive 2TB - USB 3.0
In general, G-Drive is a great company. This drive offers amazing mobile capacity, and for anyone who doesn't have one of the new MacBook Pro's, this is a great purchase!