You will need a hard drive; these come in two main types although these days one of them, the IDE drive is being replaced with the newer SATA drives. You will need to get a hard drive with enough storage to do what you want with, but at present the cost of storage is not that expensive. A 500 gigabyte or 1 terabyte drive will give enough storage for most applications.
You also need to take size into consideration if you are going to partition your drive to run multiply operating systems in the future. Modern hard drives are pretty fast and one of the common myths I keep hearing is that defragmenting your hard drive will significantly speed up your system, sorry to disappoint you but it won’t, you probably won’t notice any difference. The traditional manufactures are Seagate and Western Digital, along now with Samsung, Hitachi and Toshiba.