external harddrive for macbook pro

You've been here for NINE years, you should know better than to ask a question as vague as this! Go read the sticky about rules for successful posts here. Do you want USB, Firewire, or Thunderbolt connection? Do you want a portable drive that is powered by the laptop itself, or will it be used at home, where you can afford to plug it into a wall to get more speed (most useful, for example, when doing Time Machine backups). What size do you need? Do you have an earlier Macbook Pro with a 120GB hard drive that you just need more space, or do you have a brand new 768GB SSD that you will be running weekly Time Machine backups for, plus the ability to hold 200GB+ of music and movies? What is your budget, do you want some clearance drive from Staples or are you willing to spend for a dual 7200 RPM, RAIDed enclosure?

prozac is correct, any hard drive will work from a compatibility standpoint. It's convenient if you buy one made for Mac already, but if it isn't, then it's simple to convert it to Apple-capable. You just use Spotlight (the magnifying glass in the top right) to find the disk utility, and it will convert the hard drive however you want. You can use Apple formatting or FAT if you need compatibility with Windows computers, you can split up a single hard drive into multiple smaller ones (for example, making a 2TB hard drive into a 1TB hard drive plus two 500GB hard drives, so that one partition is for work stuff, one is for fun stuff, one is for photos, etc).