As previously stated, you'd need a 2.5-inch Serial ATA (or "SATA") hard disk for your Mac, such as a Seagate Momentus like the one found at the following link on Newegg.com for example.
One thing to keep in mind is the rotational speed of the disk - with an increase in rotational speed (for example, 7200 RPM) you may notice slightly more noise or vibration coming from your computer when compared to a disk spinning at 5400 RPM.