• Composite Video
• This is the single, "yellow" RCA plug video cable. It transmits analog video and does not support HDTV.  If you're using this cable, you're not watching High Definition.  Odds are you have a ton of these around the house, since just about every video product on the market supports it, and will typically include one of these cables for free.
  
• S-Video
• A single video cable with a strange connector that looks a little lit the old PS2 mouse and keyboard connectors. It has a metal ring with 4 metal pins inside.  It transmits analog video that is slightly better than Composite video, but it is still not compatible with HDTV.  If you're using this cable, you're not watching High Definition.
• Component Video
• This is the "the three video cables hooked together" system.  The individual cables in the set are usually color coded Red, Green and Blue, or labeled Y, Pb, Pr. It transmits analog video vastly superior to Composite and S-Video and is HDTV capable.  You can use this cable to watch High Definition.
• VGA
• The cable typically used to connect a computer to a monitor, this cable is rarely used for Home Theater applications.  It is analog and very similar in quality to Component Video cables.  Many HDTVs support it, and it it does support High Definition.   You can use this cable to watch HDTV.
• DVI
  
• The name stands for Digital Visual Interface and it's a single video cable that transmits, as the name implies, digital video.  It transmits excellent quality video identical to early versions of HDMI and is becoming more and more popular as a replacement to VGA in the PC industry.  One unique aspect of the cable is that is can transmit either Analog HDTV (which is VGA compatible) or Digital HDTV (early HDMI compatible) over the same interface.  Although it doesn't support the most recent advances in HDMI specification, it is HDTV Capable.  You can use this cable to watch High Definition.
• HDMI
• High Definition Multimedia Interface.  Another single digital video cable, but it should really be in a category of its own, because it is the only video cable that can also transmit audio.  It is the easiest and most convenient way to wire for HDTV because the one connection gets you perfect quality digital video and digital surround sound. The recently released HDMI 1.3 specification expands the capability of HDMI to support even more than HDTV, giving it perfect compatibility with the next generation High Definition video discs like HD-DVD and Blu-ray.  Needless to say, you can use this cable to watch High Definition.

Audio cables

• Stereo Audio
• These are the two, "red and white" RCA plug audio cables.  They typically complement a Composite video installation and will transmit analog, stereo audio. Although they can support matrix surround sound, like Dolby ProLogic, they do not support the discrete 5.1 surround used in HDTV (Dolby Digital) and are not recommended for High Definition Television.
• Digital RCA or Digital Coax
  
• This is a single RCA cable used to transmit digital audio.  It does support surround sound or multi channel audio and can be used for HDTV.
• Optical (TosLink)
• This is a single cable with a funny connector also used to transmit digital audio.  It has very similar capabilities to the Digital RCA cable and also supports surround sound, multi channel audio. It is HDTV capable.
• HDMI
• As of HDMI 1.3, it is the most capable HDTV audio connector.  It hasn't always supported the multi channel audio needed for HDTV, but now natively supports the lossless, perfect quality formats used on HD-DVD and Blu-ray discs.  It is the recommended cable for HDTV, both audio and video.

• Firewire or IEEE 1394
  
• Firewire is used in video for many PC and CE devices, but hasn't really penetrated the Home Theater market.  It's time may have come and gone in that space.
• DisplayPort
• DisplaytPort is the main competitor to HDMI.  It is a single cable that supports both digital audio and digital video and has its own copy protection scheme similar to HDCP called DisplayPort Content Protection (DPCP).  The specification has been approved, but products are yet to make it to market.  They are expected some time in 2008.
  
• Video over USB
• Some companies are investigating using a standard USB cable to transmit Digital Video.  It would support multiple displays by daisy chaining them together.  This sounds like neat functionality, but is still in the experimental phase.
  
• Wireless HDMI
• Many companies, such as Tzero, are actively working on a Wireless implementation of the HDMI spec, and some products are starting to hit the market.  Once this functionality is native to the devices you buy, you'll no longer need to connect anything with a cable.  Just plug them into the wall and you're ready to go.