it depends whether you want one that requires external power or not. i used to have one that did, but having a little one that doesn't is so much nicer.
i have this which i use for plugging in the back of the tv, not usb3 but very happy with it :
http://www.amazon.co.uk/Buffalo-MiniStation-Slim-Portable-Drive/dp/B008A1C0CW/ref=dp_ob_title_ce