Any external hard drive will work with PCs or Macs, as long as the connectors are there (Firewire, USB, etc.)
It doesn't matter how the drive is formatted out of the box, since you can re-format any way you like.
Formatting in HFS (Mac OS Extended) or FAT32 or NTFS-3G can be done with Mac's Disk Utility.
FAT32
- Read/Write from both native Windows and native Mac OS X.
- No individual file larger than 4GB.
NTFS
HFS
- Read/Write from native Mac OS X
- To Read/Write from Windows, Install MacDrive