Slim Devices SB3 external hard drive

I am getting ready to start setting up a Sqeezebox playback system and wondering what others are using for a hard drive. I am thinking about getting a 500 gig external drive and never owning or using one before, I don't want to buy a POS. Also should I be using another for a back up?
Any other advice for a newbie?
Thanks in advance for any and all advice
Jeff