Uh you've been asking a lot of questions lately No offense, but these are banal questions Google can answer. I bought an external hard drive from Transcend a long time ago. Still running today, but I don't use it much anymore. Today I use M-Discs, usb drives and especially internal WD gold hard drives.
Just buy any external hard drive, which is in the offer. Below I have linked you to my external hard drive and some others:
My hard drive (a newer model, but it doesn't make that much difference): StoreJet® 25M3
i'm currently using external toshiba drives to backup my three laptops. Here in germany toshiba has a quite good reputation on popular computer boards therefore 1-2 years ago i decided to use/buy drives from toshiba only.
Currently i'm using this extrnal drives to backup all my laptops (2,5 inches): *) Toshiba Canvio Alu 1TB *) Toshiba Canvio Basics 2 TB
*) Toshiba Canvio Basics 1 TB
.. also running a 'big' external drive with 3,5 inches: Toshiba Canvio 2TB
Another very reliable manufacturer of harddrives is: HGST.
If you want to go USB look into the Western Digital My Book USB backup drives. If you get one of the dual drive setups they can be set up to mirror so you will have 2 copies of your data. One goes bad, replace it, and the data will be auto restored to the new replacement drive. How cool is that?