USB
USB is the most common data interface used at this time. USB supports a very wide range of devices including external storage devices, webcams, input devices like keyboards and mice, and much more. There are many different common connections used for USB devices, but other than being physically shaped different they all provide the same function.

Serial
Serial is an older data interface that is being phased out, but is still commonly used due to how popular it once was. Serial is not nearly as fast as USB or other current data interfaces. Serial is most commonly used with a DE-9 (commonly, but incorrectly called DB-9) connector. It can also be found with a DB-25, 8-pin mini-din, and some other less common connectors.

Parallel
Parallel is a data type that uses several different connectors. Parallel is faster than serial due to it's ability to send multiple bits at a time, but is older and not as fast as USB. Parallel is being phased out and most devices are switching to the USB interface. Parallel was most commonly found being used with printers, but was also used with many other types of devices. On the computer side of the interface parallel uses a DB-25 connection. For the device side there are several common connectors such as: DB-25, Centronics, Mini-Centronics.

FireWire
FireWire is a fast data connection that is used for a wide range of devices. While it is a fairly common connection it is not as common as USB. One of FireWire's main uses is with digital video cameras, but is also used with external storage and other devices. FireWire commonly comes in both 400Mbps and 800Mbps versions. The 400Mbps version uses both a 6-pin and a 4-pin type connector. The connector for the 800Mbps version is a 9-pin connector.

Ethernet
Ethernet is used to connect your computer to other computers and the internet. Ethernet is a fast connection designed for this purpose alone. Ethernet uses an 8P8C (RJ45) connector. Ethernet speeds commonly range from 10Mbps to 1000Mbps. It most commonly runs on cat5 cable, but can also be used on cat6 and other types of cable.

GPIB
GPIB is a name for the IEEE-488 interface. IEEE-488 has been around for a very long time and is most commonly found on measurement and test equipment. IEEE-488 is a parallel type data bus. It supports up to 15 devices with a max Bandwidth of 1Mbps (up to 8Mpbs on updated equipment). IEEE-488.2 defined the commands to control equipment so that it could be standardized between different equipment manufacturers.

SCSI
SCSI is an older data interface that was used for both internal and external equipment. There is a large number of different SCSI interfaces and speeds. SCSI has always been a fast interface in comparison to other available interfaces, but has also generally been more expensive because of this. SCSI has a lot of benefits to it including the ability to hook up to 16 devices on a single bus, high speeds, error checking. The benefits from SCSI make them more commonly used in high end machines like servers where the performance is worth the extra cost.