Although technically all external hard drives should be compatible with the Mac, many brands prefer to have an exclusive product line for Mac that follows the aesthetics of Apple products.
This is the case of Hitachi, which has presented a line of hard drives that at least aesthetically are very successful, with a look very similar to the Mac Pro and possibilities for example to make RAID.
If you're thinking of getting a hard drive and don't want to break the aesthetic harmony with an ugly plastic one, this G-Technology line from Hitachi is undoubtedly a great option.
Source | TUAW