In actual use, the difference between most brands given the same type of drive, is barely, if at all noticeable.
What you can use is determined by your controller (motherboard in most cases). The major interfaces are IDE (older systems than 2 years), SATA (1 year old systems, also called SATA150), SATA2 (current systems, also called SATA300) and SCSI (requires a dedicated controler card, not standard equipment).
The latest version of SCSI (there are over a dozen) is the fastest by a bit, but the cost is many times that of the other types. Not recommended.
SATA2 as an interface has excellent performance. There are many drives on the market for it right now, and they have several features you need to look for to maximize it's performance. NCQ (Native Command Queing), a 16MB buffer (as opposed to 8 or 2) and a high rotation speed are the three big factors. Most drives have a rotation speed of 7,200rpm while the Raptor models from Western Digital are at 10,000. The Raptors are a little special, I'll touch on them below. Basically pick a SATA2 drive with NCQ and a 16MB buffer at whatever size you want - shop for a good deal or sale, they are all very similar in performance. WD, Seagate and Maxtor are the big names.
SATA is still very popular even though it was only mainstream for 2 years. It was the replacement for the older, slower IDE interface but SATA2 came along very quickly. Manufacturers however still support it with new models all the time. As with SATA2 pick a large buffer and the size of your choice. NCQ as far as I know is not available with SATA.
IDE drives used the old flat ribbon cable like optical drives now do. It's very slow in comparison and unless you don't have a choice, don't consider an IDE hard drive. Buffers went to 8MB on them.
The Raptor line was designed to replace SCSI drives on workstations as a cheaper alternative. They quickly found a home however in high end game systems due to the increased speed over any other drive at the time. Raptors only come in 3 relatively small sizes and are all only SATA. This however is not a problem, as they are still faster than any SATA2 drive, albeit not by much anymore. They only use 2 platters and use parallel head access for exceptional seek time (they find data to read much faster, less waiting). Because they spin 2,800 faster than the others, they can also move that data at a faster rate, at least when multiple files are being addressed.
Where they fall short now, is in raw throughput. A SATA2 RAID0 array can put out almost double the data in raw throughput. You want that where you are serving large files, or concurrent files - like a database or large file server. I honestly don't know how a PS swap file would be catagorized, I never tested it. I don't know if it would be accesed as a large file or lots of small files. Raptors also have a couple other drawbacks due to the 10,000 RPM speed. You can hear them, like a quiet CD burner spinning all the time - and they give off a lot of heat and need active cooling - either water or a dedicated fan on them (most cases have a fan near the hard drives).
